48 SCIENCE AND THE HUMAN MIND 



though his conclusions and theories were often wrong, 

 his methods marked a great step in advance. For 

 instance, after giving an account of the views on 

 respiration held by earlier naturalists, he points out 

 that " the main reason why these writers have not 

 given a good account of these facts is that they have 

 no acquaintance with the internal organs, and that 

 they did not accept the doctrine that there is a final 

 cause for whatever Nature does. If they had asked 

 for what purpose respiration exists in animals, and 

 had considered this with reference to the organs, e.g. 

 the gills and the lungs, they would have discovered 

 the reason more speedily." Here the insistence on 

 the need of observation of anatomical structure 

 before the framing of views on the functions of organs 

 is the point, and, in the treatment which follows, 

 Aristotle passes in review the structure of a number 

 of animals, and describes the action of their lungs 

 or gills. In drawing conclusions, Aristotle had, of 

 course, no knowledge of chemistry to help him, the 

 idea of gases other than air was unknown, and the 

 only change in air which could be suggested was 

 its heating or cooling. Aristotle's theory that the 

 object of respiration is to cool the blood by contact 

 with air, though now seemingly absurd, was perhaps 

 the best of which his age was capable. 



Aristotle took over from Plato, his master in philo- 

 sophy, many metaphysical ideas, some of which he 

 modified in accordance with his greater knowledge 

 of nature. Plato had no scientific insight ; his interests 

 were philosophical. Hence perhaps arises the fact 

 that Plato's theory of nature as a whole, and even 

 that of his pupil Aristotle, were less in accordance 



