THE MAIN GROUPS OF ANIMALS. xxiii 



notion of the relative temperatures of different animals either directly 



by touch, or indirectly by inference from structure. On touch, though 



sometimes used by him, he apparently placed b ut little reliance. For, 



as he says,* it could not tell whether the heat was intrinsT c, or whether I 



it was merely accidental and derived from without. Moreover, even 



supposing that touch were a sufficient measure of ordinary heat, it by no 



means would necessarily follow that it would be an equally good test 



of " vital heat," which was something in Aristotle's opinion quite distinct 



in its efficacy from common heat,'^ and would require to be measured by 



its own appropriate standards. He relied therefore mainly on inference q 



from structure. The presence or absence of blood, and its relative / ; /r AO'W^ 



abundance, gave him indications^ in which he had absolute confidence. 



No less certain was the evidence given by the presence or absence of a ^ aIm^K^ 



lung, and by its degree of development. For, by his theory of respira- ^ ^ 



tlon," the whole purpose of a lung was to temper the excess of heat. '' 



" Those animals," he says, " are the more perfect that have the greatetj 



amount of heat ; and in animals that have blood the measure of natural] 



heat is the lung. For those that have a lung are invariably hotter than 



those that are without one ; and among such as possess one, those in 



whom it is richly supplied with blood and soft in texture are hotter than 



those in whoni it is bladdery or hard, or contains but little blood." * r </• 



Besides thepblood and theviung, Aristotle had a third structural "~" " 



measure of temperature in thO ^brain^ which shared, as he thought, with C . t-^y^^ 

 the lung the office of reducing excess of heat. The close connection, 

 however, of the brain with the higher sense organs, and its delicate 

 sympathy ' with the heart, made its presence and size a measure of the 

 intellectual faculty rather than of the excellence of the soul as a whole. 



A fourth measure of animal heat, on which Aristotle placed great • DAfmdyiiA 

 reliance, was the condition of the embry o when liberated from the 

 mother's body.* Impressed by the manifest action of heat in effecting 

 the development of the eggs of birds and reptiles, he erroneously though 

 not unnaturally inferred that the more mature condition of the mamma- 

 lian embryo at the time of birth was mainly due to its having been 

 subjected to a higher temperature in its mother's womb ; and similarly 

 that all other ovipara must be colder than birds and reptiles, inasmuch 

 as their eggs were, as he thought, deposited in a still less advanced state. 

 This, however, we shall have to consider at greater length hereafter. 



There remains yet a fifth among Aristotle's thermometers, which, 

 almost childish as it now appears, yet requires a moment's notice. One 

 of the primary axioms upon which all his notions of the material world 



» D. P. ii. 2, 20. ' Cf. ii. 6, note 7, and D. G. ii. 3, 13. ^ D. P. iii. 6, 9. 



* D. G. ii. I, 16. * Cf. ii. 7, note 27. " D. G. ii. 1, 17, etc. 



U>^ 





