52 Greek Biology 



heterogeneous parts (avo^oio^prj} such as face, hand, and the 

 rest.' x 



The distinctions are not altogether clear but may perhaps 

 be explained along such lines as the following. The division 

 into homogeneous and heterogeneous corresponds in a general 

 way to the later division into Tissues and Organs, the former, 

 however, including much that we should not call tissue. 

 The homogeneous parts were again of two kinds : (a) simple 

 tissues or stuffs without any notion of size or shape, that 

 is, mere substance capable of endowment with life or soul, 

 e.g. cartilaginous or osseous tissues ; and (b) simple structure, 

 that is actual structure made of such a single tissue but with 

 definite form and size, matter to which form had been 

 added and which either was actually or had been endowed with 

 soul, e.g. a cartilage or a bone. 



As a physiologist Aristotle is, in fact, in much the same 

 position as he is as a physicist. He never dissected the human 

 body, he had only the roughest idea of the course of the vessels, 

 and his description of the vascular system is so difficult and 

 confused that a considerable literature has been written on 

 its interpretation. He regarded the heart as the central organ 

 of the body and the seat of sensation and he probably believed 

 that the arteries contained air as well as blood. He made 

 no adequate distinction between veins and arteries. He tells 

 us that two great vessels arise from the heart and that the 

 heart is, as it were, a part of these vessels. The two vessels 

 are apparently the aorta and the vena cava, and a very 

 elementary and not very accurate description is given of 

 the branches of these vessels. He believed that the heart 

 had three chambers or cavities and that it took in air direct 

 from the lung. 



The brain was for him mainly an organ by which were 

 secreted certain cold humours which prevented any overheating 

 1 De partibus animalium ,ii. i ; 646* 12. 



