Notes, iii. 6. 205 



this seeming inconsistency. I imagine, however, that what he would have said was this. 

 The lung provides for the general refrigeration of the heart and body at large. But in 

 order to ensure the perfection of the sense-organs (Z>. P. ii. .10, 11), it is necessary that 

 there shall be a part where the refrigeration shall be much more intense,- and this part is 

 the brain. 



4. Cf. iv. 13, Note 38. 



5. " Of all animals the strangest are the dolphins and those other Cetacea, such as the 

 whale, that have a blow-hole. For one cannot easily class them either simply as water- 

 animals, or simply as land-animals, if we define land-animals as those that- take in air, 

 and water-animals as those which take in water. For these animals do partly one, partly 

 .the other. For they take in sea- water and discharge it by the blow-hole, and they also 

 have a lung and with it take in air, etc." {H. A. viiu 2, 4). From this and similar 

 passages it is plain that A. made a distinct division of Cetacea, separating them on the 

 one hand from the viviparous quadrupeds owing to their living entirely in the "water and ' 

 having no distinct limbs, and on Jhe other hand from the fishes, owing to their having 

 a lung, true bones, and mammae. 



6. The mechanism of respiration is described elsewhere {;De J?esp. 21). ' The lung is 

 compared, aptly enough, to a pair of forge bellows. When the lung is expanded, air 

 rushes in ; when it is Contracted, the air is again expelled. The expansion is brt)ught 

 about by the heat derived from the heart ; heat always causing expansion in the parts to 

 which it extends. ■ The lung then, heated by the heart, expands ; and with it .the cavity 

 of the thorax. Cold air rushes in to fill the void, and the heat is reduced. This causes 

 the lung and thorax to collapse, and the air is expelled. 



7. The argument seems -to be this. If the motion of the heart depended on the lung, 

 then that motion should be precisely similar in all animals that have a lung. But this is 

 not the case ; for in man alone, or nearly so, does palpitation occur. A; guards himself 

 somewhat by the words ^^ so to sfeak," which is a usual form with him for ^^witk some 

 exceptions." Otherwise he is in error in saying that man is the only animal whose heart 

 is set in violent palpitation by mental emotion, as every experimental physiologist knows. 

 "In a frightened horse," says Darwin, " I have felt through the saddle the beating of the . 

 heart so plainly that I could have counted the beats" [On Expression of Eviotions, p. 

 77). The distinction between jumping palpitation (ir^STja-ty) and ordinary heart action 

 (fiXffjs and atpvynos) is elaborated in £>e Resp. 20, A. 's explanation of the heart's action 

 and of the pulse, as there given, .was as follows : The food, he says, is without intermission 

 pouring into the heart ; here it is heated ; and this heating causes it to swell, just as water 

 swells and bubbles .up when boiled. The dilatation of the heart is due to this, as also 

 (see last note) is the expansion of the lung and thorax, which leads to the admission of 

 cold air into that cavity. The entrance of air cools pot only the lung but also the heart, 

 and in consequence they both contract.- This alternate expansion and contraction of {he 

 heart extends to the blood-vessels (i.e. arteries and veins), as they are continuous with the 

 heart, and the blood within them is affected by the changes of heat in thie same way as 

 that in the heart. Thus the blood-vessels throb simultaneously with the heart, and aU'at 

 the same moment. The internal heat is greater in youth than in after-life (ii. 2, Note 

 10) ; consequently the whole process described, which is due to this heat, takes place 

 more rapidly at that period *of life;. and this explains why the pulse is more rapid in 

 youth than in after-life. Aristotle also- compares the beating of the heart to the throbbing 

 felt in a swelling while puS is yet being formed, this throbbing like the pulsation being 

 due to concoction ; for, as soon as the pus is concocfed and fully formed, the throbbing 



.ceases. 



