FATHERS OF BIOLOGY. 



the air cools it and carries off its superfluous heat. Some 

 of the air which enters the lung gets from the bronchial 

 tubes into the blood-vessels by transudation, for there is 

 no direct communication between them; and this air, 

 penetrating the body, rapidly cools the blood throughout 

 the vessels. But Aristotle did not consider the "pneuma," 

 which thus reached the interior of the blood-vessels, to 

 be exactly the same thing as air it was " a subtilized and 

 condensed air." l And this we now know to be oxygen. 



The treatise " On the Generation of Animals " is an 

 extraordinary production. " No ancient and few modern 

 works equal it in comprehensiveness of detail and pro- 

 found speculative insight. We here find some of the 

 obscurest problems of biology treated with a mastery 

 which, when, we consider the condition of science at 

 that day, is truly astounding. That there are many 

 errors, many deficiencies, and not a little carelessness in 

 the admission of facts, may be readily imagined ; never- 

 the less at times the work is frequently on a level with, 

 and occasionally even rises above, the speculations of 

 many advanced embryologists." 2 



It commences with the statement that the present 

 work is a sequel to that " On the Parts of Animals ;" and 

 first the masculine and feminine principles are defined. 

 The masculine principle is the origin of all motion and 



1 See Professor Huxley's article already referred to. 



2 "Aristotle," by G. H. Lewes, p. 325. 



