40 THE HISTORY OF BIOLOGY 



lion; in fact, he says of this animal that it has no cervical vertebras, but in- 

 stead has a single conjoining bone. In another place he declares of a lion's 

 bones that they are so hard that they give off sparks when struck, like flint, 

 and that they are "said" to have no medullary cavity. How much Aristotle 

 in general borrowed from the wisdom of his predecessors it is impossible to 

 determine, as their writings have been lost and he never quotes others except 

 with polemical intent. But examples such as those cited above undoubtedly 

 testify to a quite uncritical exploitation of foreign sources, and it is manifest 

 that the value of Aristotle lies not so much in the facts he established as in 

 the systematic working-up of the scientific material he had at his disposal. 

 And this systematizing work of his was of course as comprehensive as was 

 possible with the means available at the time. It is not only the outward 

 form of animals and their existence that interests him; he studies the migra- 

 tions of birds and the wanderings of fishes and tries to discover the causes 

 that underlie these habits; he critically examines the outward manifesta- 

 tions of animal intelligence, and everywhere he closely compares different 

 forms of life. 



He chiefly occupies himself, however, with the anatomical and mor- 

 phological structure of animals, as well as with their reproduction and 

 evolution. These two spheres of investigation he has elaborated with the 

 utmost care, and here we find he stands out most prominently as the founder 

 of comparative natural philosophy. His t/eatises on human anatomy have 

 been lost, but his great descriptive work on animals is extant and deals 

 mainly with anatomical questions. Here he at once, in the very beginning of 

 the work, lays down that anatomical research should be comparative; the 

 less known should be studied by comparison with the better known, and 

 since the structure of the human body is best known, that should be the 

 point of departure. Following this method, he goes through the parts of the 

 body, the external as well as the internal. He bases his general anatomical 

 ideas on the same principles as Empedocles and the Hippocratic writings, 

 and certainly also as Democritus. With the first-mentioned he holds that all 

 beings are composed of four elements, while for him, too, the contraries hot 

 and cold are of fundamental importance. His description of human anatomy, 

 which forms the first book of his work on animal life, is of unequal value 

 and, as regards its details, undoubtedly very much dependent upon the state- 

 ments of others; but his manner of summarizing his description is excellent. 

 As to his description of the internal anatomy, he frankly acknowledges that 

 it is founded upon conclusions drawn from the dissection of animals, and, 

 broadly speaking, it is not very different from the Hippocratic writings re- 

 ferred to above. Thus the heart is to Aristotle the organ of the soul and the 

 intelligence, the brain serves the purpose of producing mucus and cooling 

 the blood; in this respect his ideas are inferior to those of both Democritus 



