¿Por qué los Hombres tienen diversas Maneras de Ojos? Curiosities about the Eyes in Juan de Jarava’s Problemas o Preguntas problemáticas (1544)

Abstract

The so-called ‘problem books’ of the 15th and 16th centuries originate from the pseudo-Aristotelian Problemata, which were rediscovered around 1300. Their authors were often physicians who prepared medical information for a broad public and combined it with highly heterogeneous pools of knowledge. This article deals with different questions in regards to the eye and the sense of sight in Juan de Jarava’s Problemas o Preguntas Problemáticas, published in 1544. The physician, a man with Erasmist inclinations whose existence remains a mystery, divides his work into three parts, with each relating to love, natural phenomena, and wine. In all three parts, questions related to the eyes are raised. These issues are contextualized in the scholarly discourse of the time in order to determine to what extent Jarava is representative of knowledge about the eyes in the early modern period. The example of vision and the eyes can be used to show how early modern medical writers such as Juan de Jarava and Agustín de Ruescas tackled the complexity of the world in their problem books.

1. Early Modern ‘Problem Books’ in Context

In the 21st century, it is second nature to simply Google all sorts of questions that may arise during the course of the day. In the 16th century, any and all possible queries were collected in so-called problem books, which, like modern search engines, also held the appropriate solution at the ready. These books originated from the pseudo-Aristotelian Problemata, which were rediscovered around 1300.1 Their authors were often physicians who prepared medical information for a broad public and combined it with highly heterogeneous pools of knowledge. The thematic field of the eye and vision is wide ranging in these works, not only in terms of content, but also in terms of architecture. Oikonomopoulou, who has studied the structure of medical books of the pseudo-Aristotelian collection, notes that “the authors of the Problemata took care to organise medical problems into books according to topic”, but “far from offering an orderly exposition of their respective topics, [they] give the impression of disjointed assemblies of heterogeneous causal enquiries” (Oikonomopoulou 2015, p. 61). The quoted scholar’s reflections on ‘meandering sequences’ are extremely stimulating and of heuristic value for the discussion of later problem books. She proposes that they “might be tied to the cognitive processes and patterns of scientific research that were adopted by the different authors who gave input to the Problemata’s medical books: free to take up, develop in different directions, or re-consider various lines of enquiry, they left a vast record of overlapping sets of problems and solutions on select medical topics” (Oikonomopoulou 2015, p. 65). As far as vision is concerned, the 31st book is dedicated to the eyes, but the 3rd book, concerning wine-drinking and drunkenness, also deals with phenomena relating to seeing.2 In the book about the eyes, some issues are treated twice, a point to be returned to in the comparison with Juan de Jarava.

In the following years, a number of different problem books significant with regard to Jarava’s work were written. One of them, attributed to Alexander of Aphrodisias, was translated several times from Greek into Latin. The versions by Giorgio Valla and Theodorus Gaza circulated in printed editions.3 Worthy of mention in our context is also a group of Greek problemata ascribed to Cassius the Iatrosophist and printed in Paris by Christian Wechel in 1541 in a Latin translation by the Dutch physician Adriaen de Jonghe.4

Of the Latin problem books written partly on the basis of the forementioned material, two are of relevance in our context; firstly the Quæstiones Quædam Naturales cum Amatoriis Problematibus XX, by Niccolò Leonico Tomeo (1525), hellenist and translator of Aristotle (Fortuna 2010), who was also much appreciated by Erasmus (Russo 2005).5 The second is the Aristotelis ac Philosophorum Medicorumque Complurium Problemata of Marco Antonio Zimara, a very popular work that has seen 26 editions since the 1536 princeps and has been translated into various vernacular languages (Celati 2020).6

The first vernacular problem book was written by a physician from Bologna.7 The structure of this work is different from that of the several authors of the pseudo-Aristotelian Problemata. While the latter proceeded accumulatively, the Italian doctor organized the parts more consciously.8 As Nada Patrone (1988, pp. 29–30) has shown, Girolamo Manfredi draws from the pseudo-Aristotelian Problemata, but he is in general, more wordy, often repeating, albeit in different chapters and with expository variations, the same questions without respecting the arrangements of his model. Manfredi divides his Liber de homine or Il perché into two books. The first one is about the preservation of health, following the traditional pattern of the sex res non naturales. The second book deals with the parts of the body and thus, also with the eyes, to which 54 questions are dedicated.9 In Aristotle, including repetitions, there are only 29 questions related to this issue. This increase can mainly be ascribed to the great interest that the Italian shows in physiognomics.

The first book of problems written in Spanish by a physician is the Libro Intitulado los Problemas, by Francisco López de Villalobos (1543).10 He says nothing regarding the eyes or vision here, although he deals intensively with ophthalmology in the Sumario de la Medicina (López de Villalobos 1498). Another medical doctor, Agustín de Ruescas, published a versified problem book in dialogue form a little later (Dialogo en verso Intitulado Centiloquio de Problemas, Ruescas 1546), in which we find a number of questions concerning the eyes, to which we will return in more detail later.

2. Problemas o Preguntas Problemáticas by Juan de Jarava

Juan de Jarava, the author of the Problemas o Preguntas Problemáticas, the object of our study, was also likely a medical doctor (Sanz Hermida 1998, p. 629). The confirmed biographical data about him, however, are so sparse that some researchers have even assumed that the name was merely a pseudonym of Francisco de Enzinas.11 Most of his books were published in the Low Countries. The printer of his problem book, published in 1544 in Louvain, was Rutger Rescius, a friend of Erasmus who usually specialized in Latin and Greek works (Bietenholz and Deutscher 2003, III, pp. 142–44). Jarava’s work must have been quite successful because it prompted a new edition two years later in Alcalá de Henares with Juan de Brocar (Jarava 1546).

Jarava has primarily emerged as a translator. He rendered works by Lucian12, Erasmus, and the Protestant botanist Leonhard Fuchs (López Piñero and López Terrada 1994) into Spanish. Even Problemas o Preguntas Problemáticas, thought for a long time to be an original work by the author, is actually—at least in part– a translation. As recently noted by Sanz Hermida (2017, p. 221, note 9), the work is largely based on Leonico Tomeo’s Quæstiones. Problemas o Preguntas Problemáticas, which is divided into three parts, each dealing with love, natural phenomena, and wine.13 19 of the 20 questions on love14 and 79 of the 226 “Demandas Naturales” can be traced back to the Italian Erasmist. One of the few quaestiones by Leonico Tomeo that Jarava does not translate is interestingly the one on the basilisk, the mythical creature that is equal to no other regarding the poisoning power of its gaze (Sanz Hermida 2001, pp. 22–23).

2.1. Love and Vision in Problemas o Preguntas Problemáticas

Despite the subdivision into three thematic areas, the topics of Problemas o Preguntas Problemáticas are jumbled up in a haphazard way, as often occurs in problem books. In the first part, there are four quite different questions that have to do with the eyes. The first of these, which also opens the collection, asks: “¿Por qué los que aman se prenden y toman del amor por los ojos de las que aman mas que por otra parte ninguna del cuerpo?” [Why do those who love take hold of love through the eyes of those they love more than through any other part of the body?] (Jarava 1544, f. A7v). Following Leonico Tomeo, different solutions are proposed. Initially, the eyes are identified as the organs that, like no other, reveal the emotions15 and are capable of attracting lovers with a ‘bond of passion’ (“lazo de deseo”, f. A7v). In the second part of the answer, the eyes are referred to as the domicile of the soul, as well as its messenger (“morada y aposento del alma”, “mensajeros de ella”), whereas love is designated as “afeción del alma” [affection of the soul]. The longing for the soul of the beloved thus explains the joy that lovers feel when they gaze at each other. In the third part, the argumentation changes fundamentally, and with recourse to Lycophronides, modesty is described as a woman’s most beautiful adornment. And Aristotle is quoted as a source for locating modesty in the eyes.16 The poorly consistent argumentation, which goes back to Leonico Tomeo, may be explained by the latter’s recourse to The Deipnosophists, or Banquet of the Learned, of Athenaeus of Naucratis.17 This has no discernible connection with the following reference to the poets’ depiction of Cupid:

Quamobrem & poetae qui ex amatorum oculis Cupidinem spicula in amantes iaculari cecinerunt, aut inde faces accendere quibus illos exureret, haud absurde rei ipsius naturam expressisse uidentur. [This is why one should not despise the way this matter was depicted by the poets, as they portraited Cupid shooting arrows from the beloved-ones’ eyes against the lovers, or setting trusses of straw alight in order to burn them up].

(Leonico Tomeo 1525, f. LVIr)

As a connoisseur of Greek literature, the Italian was possibly thinking of texts such as Heliodorus’s novel Aethiopica. Here, Kalasiris explains to the father of the lovesick Chariclea how this form of evil eye is transmitted:

Conclusive proof of my point is furnished by the genesis of love, which originates from visually perceived objects, which, if you will excuse the metaphor, shoot arrows of passion, swifter than the wind, into the soul by way of the eyes. This is perfectly logical, because, of all our channels of perception, sight is the least static and contains the most heat, and so is more receptive of such emanations; for the spirit which animates it is akin to fire, and so it is well suited to absorb the transient and unstable impressions of love.

(Heliodorus 1989, p. 25)18

The passage in which Leonico Tomeo speaks of “Cupidinem spicula” has been slightly modified by Jarava, who writes:

Por lo cual también los poetas que dijeron que Cupido, dios de amor, echaba de los ojos de las enamoradas en los ojos de los amadores unas como saetas, parecen haber declarado que se encendían de allí hachas que los quemaban como fuego. [For this reason the poets who said that Cupid, god of love, threw from the eyes of the lovers into the eyes of the lovers, some like arrows, seem to have declared that torches were lit from there that burned them like fire].

(Jarava 1544, f. A8r)

The agency of the god of love and the use of his arrows could have been familiar to Jarava from Spanish texts such as Luis de Lucena’s Repetición de amores –”Este mozo es muy poderoso en llamas y saetas” [This young man is very powerful in flames and arrows] (Lucena 2001, p. 109); “Resta agora declarar las cosas que los poetas atribuyen a Cupido, e son que es mozo, con alas, con arco e saetas, con hachas ardientes, con corazones atados en la cinta e con la venda de paño atada sobre los ojos” [Now it remains to declare the things that the poets attribute to Cupid, and they are that he is handsome, with wings, with a bow and arrows, with burning torches, with hearts tied in a ribbon and with a band of cloth tied over his eyes] (Lucena 2001, pp. 117–18)—or the Celestina (“aquella ardiente llaga que la cruel frecha de Cupido me ha causado” [that burning wound that Cupid’s cruel arrow has inflicted on me], Rojas [1499] 2000, p. 90) to name but a few.

The much-discussed subject of the origin of love is dealt with in both texts in just a few lines and accompanied by a terse reference to “the poets”. It is worth stressing that Marsilio Ficino’s widely received Neoplatonic theory of the origin of love through the rays of the eyes is not taken into consideration.19 Even though Leonico Tomeo, who published an annotated translation of the Parva naturalia in 1523, was perhaps closer to Aristotelian ideas, scholarship has highlighted his attempt to reconcile Aristotelianism and Platonism (De Bellis 1975, pp. 73–74; Russo 2005; Holland 2020). It can be assumed that Leonico Tomeo is alluding here to the Platonic concept of perception. As Lindberg has shown in his still relevant study on vision, “the theory of intraocular fire reached its full development with Plato”, who elaborated on it, for instance, in Timaeius (Lindberg 1976, p. 5).20 However, this does not happen in the context of notions of love. A much-discussed precursor of the Platonic theoretical framework was a poem by Empedocles (perhaps an explanation for the “poets” mentioned by Tomeo) in which Aphrodite is named as the creator of the eyes (Lindberg 1976, p. 4).21 We are concerned here with a reflection on which Aristotle also took a critical stance. It could be conceivable as well that Leonico Tomeo was reminded of the theory of love in Guido Cavalcanti’s complex canzone “Donna me prega”, discussed by two physicians, Dino del Garbo and Marsilio Ficino.22 In any case, it seems to me that Jarava, through his free translation, has suppressed the theoretical subtleties of his Latin model and, through the reference to Eros and his arrows, has invoked a far more concrete realm of imagination. There is no evidence in the Preguntas Problemáticas that Jarava was aware of the tension between Platonic and Aristotelian thought inherent in the work of his Italian model.

The seventh question, which seeks the reasons for the frequent weeping of lovers (“¿Por qué los enamorados suelen ser inclinados a llorar?”, Jarava 1544, [7], f. B4v) is explained quite simply by humoral theory and the natural moisture of the eyes from which the tears originate. Most likely Lenico Tomeo is guided by Aristotelian ideas, according to which the eyes are primarily made of water.23

The answer to the quite peculiar question about the swelling of the eyes during coitus is far more complex.24 Here, as with the first question, three possible reasons are given that call different authorities into play. The first part operates with the heating of the body, which would fill the pulse and the arteries, what is first and most clearly recognizable through the eyes as the “doors of the soul”. With quotations from Homer25 and Democritus, Leonico Tomeo proves himself to be a fine maven of Greek antiquity. Aristotle endorses the presocratic philosopher’s theory that the eyes are made of water.

In another quaestio, Leonico Tomeo, followed by Jarava, is primarily oriented towards Plato. Investigating the problem of why lovers do not see the vices and defects in the body and soul of the ones they love, it is argued, with recourse to Platonic doctrine, that the very great movement of the spirit hinders the senses, and the person in love is blinded by the thing they love. This also explains why the poets considered Cupid, god of love, to be blind.

By drawing on Leonico Tomeo, Jarava has reworked and vulgarized ancient Greek reflections on the connection between physical and spiritual love and vision for a broader Spanish audience.26

2.2. Vision in Juan de Jarava’s Questions on Nature

The natural questions concerning the eye and vision, 16 in total, cover different issues, such as the anatomy of the eye (94), the visual perception (59, 60, 131, 141, 177, 201, 213), and tears and crying (123, 132, 137, 159), among several others. They are hard to categorize.27 Two of these quaestiones, like those on love, stem from Leonico Tomeo (59 and 60), while two others are taken from another modern author, Marco Antonio Zimara (94, 95), who also dealt with the issues of the aforementioned problems 59 and 60. The lion’s share, however, harkens back to ancient sources, namely the pseudo-Aristotelian Problemata (123, 130, 131, 132, 133, 141, 159, 213) and those of the pseudo-Alexander Aphrodisias (169, 172, 177).28

An interesting example of the imitation of Leonico Tomeo is the 59th question on photopic and scotopic vision related to the color of the eyes: ¿Por qué los que tienen los ojos garzos no veen bien entre día, y de noche veen mejor y por el contrario, los que tienen los ojos negros, de día veen bien, y de noche mal? [Why is it that those with black eyes do not see well during the day and see better at night, while those with black eyes see well during the day and poorly at night?].29 It is once again a presocratic that the Italian hellenist incorporates into his argumentation and which thus gains entry into the Spanish text:

La causa es: porque –como dice Empédocles– en los ojos garzos hay mucho fuego y en los negros mucha agua, por lo cual los ojos garzos, por falta del humor de agua, no pueden bien ver de día y de noche veen mejor los ojos negros por el contrario por la falta del fuego ven mejor de día que de noche. [The reasons are: because—as Empedocles says—in blue eyes there is much fire and in black eyes much water, so that blue eyes, for lack of the humour of water, cannot see well by day and black eyes, on the contrary, for lack of fire, see better by day than by night].

(Jarava 1544, ff. F8v-G1r)

The source may have been Empedocles himself, or more likely Aristotle discussing his theses in On the Generation of Animals.30 A very similar reasoning is also found in the pseudo-Aristotelian Problemata.31

¿Por qué los hombres tienen diversas maneras de ojos? [Why men have different eyes] So reads one of the various questions about the eyes posed by Juan de Jarava, that goes back to Zimara’s Aristotelis ac Philosophorum Medicorumque Complurium Problemata, that are translated almost literally:

Respuesta. La causa es –como dice Aristóteles– la diversidad de humores, porque en los ojos hay cuatro telas y tres maneras de humores. Y la primera tela se dice consolidativa; la segunda cornea, a semejanza del cuerno y es clara; la tercera uvea a semejanza de una uva grande; la cuarta se dice tela de araña. Ansí el humor primero se dice albugineus blanco a semejanza de clara del huevo; el segundo glacialis a semejanza del hielo; el tercero vitreus a semejanza del vidrio claro. Esta diversidad pues de humores causa diversidad de ojos. [Answer. The cause is, as Aristotle says, the diversity of humours, because in the eyes there are four tunics and three kinds of humours. And the first tunic is called sclera; the second cornea, in the likeness of the horn and is clear; the third uvea in the likeness of a large grape; the fourth is called spider’s web. Thus the first humour is called albugineus white in the likeness of egg white; the second glacialis in the likeness of ice; the third vitreus in the likeness of clear glass. This diversity of humours causes diversity of eyes]32.

Jarava, like Zimara,33 explicitly quotes the Stagirite as authority, although he had no such specialized knowledge. Kalderon refers to the Aristotelian anatomy of the eye as “crude, even by ancient standards” (Kalderon 2015, p. 163). As Lloyd details, “there is no mention of the membrane enveloping the vitreous humour (retina, choroid, sclera), nor of the lens, nor of the anterior chamber between the cornea and the lens” (Lloyd 1978, p. 221).34 Zimara’s description of the eye, however, goes back to Galen or to Alhacen (ca. 965–ca. 1040), who built on the former’s teachings.35 The Islamic scholar played a leading role in the further advancement of the knowledge of the eye,36 although the extensive work was slow to become known in Europe.37 Alhacen’s theories were popularized by widely read and often printed books such as De Proprietatibus Rerum by Bartholomaeus Anglicus.38 The fifth book, which deals with the human body, contains several chapters on the eyes. The fifth chapter provides a description of the humores and tunicae, which resembles the conception of the Islamic scholar.39 The condensed account of the medieval encyclopedia is closer to Zimara’s text than the detailed expositions of Galen and Alhacen.40 It is worth noting that Bartholomew also mentions Alhacen in the third book in the chapter “De Virtute Visibili”.41 Interestingly, he refers to him as “a philosopher”42, possibly as an explanation for the fact that his ideas were attributed in 16th century problem books to the Stagirite, who is often just called “the philosopher”. This long digression has shown the complex ways in which knowledge about the eye found its way into the works of authors such as Juan de Jarava. At this point, we can state that the use of specialised terminology is present in those ‘problems’ that can be traced back to contemporary authors like Zimara, or they are nested in the translations of ancient authors, as will be shown below.

With reference to the pseudo-Aristotelian Problemata, the following questions are discussed: Why do onions make you cry?43 Why does anger redden the eyes and shame the ears?44 Why are tears hot when you cry and cold when you have an eye infection?45 Why do you see better against the light with the hand in front of the eyes?46 Why does eye disease make you see sharper?47 And why do we stop sneezing by rubbing our eyes?48 Two of the questions also raised in the Problemata concern the interaction of the two eyes. They ask: Why do you see better with one eye closed49, and why can’t we move one eye without the other?50 The pseudo-Aristotelian text is, in these two cases, very freely adopted and heavily altered. In the modifications, interestingly, technical vocabulary is introduced to describe the structure of the eye, which is not contained in the model. In the first case, the question is the same as in Problemata XXXI, 2 (“Why do we see more accurately with one eye than with two?”), where the following argument is made: “Is it because more movements occur in two eyes, as in those who suffer from strabismus? Therefore the movement (of the two eyes) is not one, but that of the one eye is simple. So they do see less clearly” (Aristotle 2011, II, p. 317). The answer to the same question is quite different in Jarava:

La causa es: porque entramos los ojos proceden de un mismo principio, por lo cual, cuando se mueve el uno de los ojos, se mueve también aquel principio, el cual movido es necesario que haga mover el otro ojo, pues cerrando el uno de los ojos se pasa toda la virtud del ver de aquel al otro que está abierto, y como el principio no mueva más del un ojo, es necesario que aquel vea más y más cierto siendo la virtud mayor. [The cause is: because we enter the eyes proceed from the same source, therefore, when the one eye is moved, that source is also moved, which, when moved, must move the other eye, for when the one eye is closed, all the virtue of seeing is passed from the one to the other which is open, and since the source does not move more than one eye, it is necessary for the other to see more and more, the virtue being greater].

(Jarava 1544, [131], ff. L4v-L5r)

The Spaniard is much closer to Manfredi than to Aristotle in this answer.51 Both early modern physicians are quite obviously under the influence of Galenic doctrine, as confirmed by Siegel’s presentation of the issue at stake:

Galen thought that after the loss of one eye the vision of the remaining eye was enhanced, since under normal conditions the cerebral pneuma was flowing from the brain to both eyes through the interconnection of both optic nerves at their crossing, the chiasma […]. He drew from observation the faulty conclusion that we can see better with one eye when we close the other eye, since pneuma flows in larger quantities via the chiasma to the active eye.

(Siegel 1970, p. 64)52

Galen dedicates the tenth book of The Usefulness of the Parts of the Body to the eyes.53 Here, the physician from Pergamon also sets out his idea of the intersecting optic tracts to which Jarava refers in question 213 (Why can’t we move one eye without the other?):

La causa es: porque los nervios ópticos que causan la vista y que llevan el espíritu y aire luciente a los ojos proceden de un mismo principio del cerebro y cuando se juntan hacen una figura como la X y después apartándose va cada uno a cada niña de los ojos. Por lo cual viene que cerrando el uno de los ojos que todo el espíritu animal se pasa al otro ojo y que resplandece y centella con mucha luz y este es buen remedio para que salga la paja o polvo que por el viento se ha entrado en alguno de los ojos. [The reason is: because the optic nerves that cause sight and that carry the spirit and bright air to the eyes come from the same source of the brain and when they come together they make a figure like an X and then moving apart each one goes to each pupil. Therefore it comes that by closing one of the eyes that all the spirit is passed to the other eye and that it shines and sparkles with much light and this is a good remedy so that the straw or dust that has entered one of the eyes through the wind can come out].

(Jarava 1544, [213], ff. Qr-v)

Without excluding the possibility that Jarava is referring to an author who himself modified Pseudo-Aristotle, it is important to highlight his understanding of the Galenic theory of optic nerves and the Chiasma opticum.54

Some of the questions going back to Pseudo-Alexander were also popular in other problem books. Early modern readers were obviously preoccupied with issues such as “Why do we have five senses?”55 Why do you see a strike earlier than you hear the sound it makes?56 or Why don’t we see anything when we go from dark to light or from light to dark?57 The influence of light conditions on the eyesight had aroused Galen’s interest as well. In the tenth book of On the Usefulness of the Parts of the Body, he elucidates the issue with a historical account:

And I dare say you have never heard that Dionysius, tyrant of Sicily, built a chamber above his prison, a chamber that was completely covered with shining chalk and very bright in other respects too; that he brought his prisoners up into this chamber after a protracted stay below; and that they, coming into bright light from deep, long-continued gloom would of course gladly look up to the light and as they did so, would be blinded, unable to endure the sudden, instantaneous onslaught of brilliance.

(Galenus 1968, II, p. 473)58

The narrative example is not only indicative of the framing of the medical discourse, but it also shows in our concrete case that Manfredi in Il Perché bases his explanations on Galen and also adopts the tyrant’s light prison as an illustration (Manfredi [1474] 1988, I, ii, 15, p. 198).

2.3. The Influence of Alcohol on the Eyes

In the Demandas del Vino, two quaestiones deal with the influence of wine consumption on vision. These are questions that also intrigue today’s Google users, who frequently query the causes of alcohol-induced diplopia, a question already raised by the Pseudo-Aristotle authors (Aristotle 2011, III. 10, I, pp. 109–11) and by Agustín de Ruescas (1546, ff. XVr-v). Jarava, instead, wonders why in the inebriated state everything seems to revolve around the drunken viewer (Jarava 1544, [14], f. S2r). The same puzzle also engaged the Pseudo-Aristotle59 and the Pseudo-Alexander (Alexander of Aphrodisias 1513, II, 67, f. 270r) authors. The Spanish doctors distance themselves from the Aristotelian Problemata in their explanations of drink-related visual disorders and integrate their knowledge of the Galenic theory. Jarava, whose answer is mainly inspired by Alexander of Aphrodisias, refers to the optical nerve, which is not mentioned by his model.60 For his part, Ruescas draws on the pneuma for his laconic explanations:

El fluctuoso movimiento

del visivo espíritu hace

tal se estime

que antes del apartamiento

de la una forma si os place

otra se imprime.

(f. XVv)61

3. Conclusions

Ruesca’s attempt to popularize knowledge in verse deserves attention as such62. With regard to the knowledge about vision, the marginal notes are of outstanding importance. In this case, they refer not only to the Pseudo-Aristotelian Problemata, but to medieval medical literature, including that of Peter of Abano and the commentary of the Canon of Avicenna by Gentile da Foligno. It can thus be observed that two Spanish physicians, who published at almost the same time, took very different paths in their respective problem books, not only in terms of form, but also with regard to their sources. And also as far as the choice of topics is concerned, there are very different emphases, as will be shown in the conclusion by way of an example concerning vision. Unlike Ruescas, Jarava makes no mention of the evil eye63, a topic that had been intensively discussed, not only by demonologists, but also by doctors64. In his Problema LXXXVIII, Ruescas wonders why some people bewitch small children, horses, and crops. In his response, he attributes the blame to the poisonous spirits thrown from the irate eyes:

De grave odio concitados

o de lo bueno invidiosos

se aficionan,

lanzan con ojos airados

espíritus venenosos

que inficionan.

(Ruescas 1546, f. XXIIIIv)65

The overly concise exposition is based on a large number of ancient and medieval authorities, most of which do not feature in Jarava’s work, namely in this order: Aulus Gellius, Pliny the Elder, Gaius Julius Solinus, Alexander of Aphrodisias, Avicenna, Algazel, Albert the Great, and Thomas Aquinas. There are also two contemporaries quoted, namely Antonio de Cartagena, author of Libellus de fascinatione, published in 1530 (Salmón and Cabré 1998; Sanz Hermida 2001) and the Portuguese Antonio Luiz (Pérez Ibáñez 2015). The contrast of the simple patterned text with the extensive bibliographical references in the marginal gloss show how problemata literature attempted to cope with the complexity of the world. The problem books by almost forgotten authors such as Agustín de Ruescas and Juan de Jarava, which have been unfairly overlooked by scholarship, show not only what kind of knowledge about the human eye and vision was available in the early modern period, but also how this knowledge was processed and circulated.

It is striking that in the work of medical practitioners, there is a colourful mixture of scientifically sound theses with commonplaces and curiosities. It would certainly have surprised Juan de Jarava and Agustín de Ruescas that a 21st century reader would comb through their works in search of a particular topic such as the eye. Their concern was diametrically opposed to this way of reading, for they have quite deliberately not published one book on ophthalmology and another, say, on the theory of love. The blending of different topics and different approaches to one topic are the core of early modern problem books. This is what makes these books so compelling as a source of information about the variety of ideas circulating about the eye and vision during the 16th century.