CLASSICAL ANTIQUITY, MIDDLE AGES 41 



ind Plato. The circulatory system is described in the same way as in Hippoc- 

 rates. The various parts of the digestive canal are described in some detail, 

 but as regards the physiology of the digestive process he has extremely 

 primitive and vague ideas, which is not to be wondered at, seeing that 

 the science of chemistry did not yet exist. "Cooking" plays the essential 

 part in his physiology. The food is "cooked" in the intestinal tube; the 

 heart pulsates through the regular "ebullition" of the blood. With regard to 

 the nervous system his notions are equally vague; as is indicated above, the 

 brain is cold, the spinal marrow is hot; nerves and tendons are confused. The 

 aural cochlea is described, as are also the membranes of the eye; the moisture 

 of the eye is believed to receive the visual impressions. It is curious to note 

 the amount of popular superstition that is accepted, as, for instance, predic- 

 tions read from the lines of the hand, or the idea that flat-footed people are 

 of a treacherous disposition. In the comparative anatomy and morphology 

 of animals Aristotle shows his many-sided interest in all kinds of life-forms 

 and his immense power of combining observations of various qualities with 

 striking characteristics. "Four-footed beasts which produce their young 

 alive have hair; four-footed beasts that lay eggs have scales." "A single- 

 hoofed animal with two horns I have never seen. . . . No animal has at the 

 same time tusks and horns." He also makes many sound observations re- 

 garding birds and reptiles, as, for example, in reference to the outer structure 

 of the sensory organs. A distinction is made between whales and fishes, and 

 the gills forming the breathing-apparatus of fish are described with emphasis 

 on the difference between osseans and sharks. Of the lower animals — the 

 bloodless, as Aristotle calls them, after the example of Democritus — the 

 ink-fish in particular is minutely described, many carefully observed details 

 being given. Crayfish, too, and insects are cleverly described in part, though 

 with some inaccurate details. 



Reproduction of animals asexual and sexual 

 In his work on the reproduction of animals Aristotle differentiates between 

 animals which reproduce themselves by sexual means, by asexual means, 

 and by spontaneous generation. The latter occurs in a number of lower 

 animals which are produced out of putrefying substances; among these are 

 specially mentioned certain insects, such as fleas, mosquitoes, and day-flies 

 (other insects, such as grasshoppers, wasps, and flies, have sexual reproduc- 

 tion). Among the shell-fishes some are produced by asexual means through 

 bud-formation, others through self-generation. The possibility of this latter 

 method is explained by the fact that the whole of nature is full of life-spirit 

 or "soul"; this, under certain circumstances, gives form to the inanimate 

 matter and so gives rise to new beings. Sexual reproduction, again, is due to 

 the occurrence of male and female individuals. Of these two the male — or 

 more properly the man, for Aristotle takes as his starting-point here, as 



