PHENOMENA OF HEAT AND SOUND. 75 



that there was a relation between the quantity of animal 

 heat, which he considered to be something different from 

 ordinary heat, and the nature of the soul or vital principle 

 of an animal. He says that in animals a nobler soul or 

 vital principle must necessarily be associated with a greater 

 amount of heat.* 



He does not say much about the way in which he 

 believed that the animal heat was generated, but, after 

 deciding that it is not produced as a result of respiration, 

 says that it is rather from the food that heat is produced, t 

 He not only believed that heat was not produced as a result 

 of respiration, but, as will be seen further on in this chapter, 

 that respiration had a cooling effect. 



Animal heat plays an important part in the digestion of 

 food, as is well known, but Aristotle believed that it actually 

 effected digestion. I Further, he believed that it had some 

 vital influence, being different from the heat from a fire. 



He refers to the necessity for regulating the heat of an 

 animal and guarding against the destructive effects cf exces 

 sive heat. || Very small animals and those without blood 

 are sufficiently cooled, he says, by the air or water in which 

 they live, for they have but little heat. IT Fishes and other 

 animals with gills and blood are cooled by water flowing 

 over the gills through which the blood passes from the 

 heart.* 31 In mammals, birds, reptiles, and amphibians, the 

 regulation of heat is effected mainly by means of the lungs, tt 

 the air flowing through ramifications of the bronchial tubes, 

 which run so closely alongside the branches of the blood 

 vessels in the lungs that the blood is cooled and some air 

 actually finds its way into the blood, which is also cooled 

 thereby. 1 1 



According to Aristotle, the lungs were not the only 

 heat-regulating means, in animals with blood. The brain, 

 which he did not regard as the sensory centre, was believed 

 by him to have as its most important function the regulation 

 of the heat of the body, and especially the heat of the head, 

 where the chief sensory organs are situated. 



Several interesting instances of the application of heat 

 in the arts are described by Aristotle in various parts of his 



* De Eespir. c. 13. 477. t Ibid. c. 6, 473a. 



| P. A. ii. c. 3, 650a. G. A. ii. c. 3, 7366 and 737a, 



|| De Eespir. c. 8, 4746. H Ibid. c. 9, 4746. 



** Ibid. c. 21, 4806. ft Ibid. c. 15, 478a. 



H H. A. L c. 14, s. 3. P. A. ii. c. 7, 653a and 6, 



