194 Notes. \\\. 4. 



His predecessors (//. A. iii. 3,. 5) had said that the origin of the vessels was in the 

 head ; but it does not appear clearly what they meant by origin, or whether they used 

 the term in the same sense as did Aristotle. This much, however, geems certain : that 

 they regarded the heart as no ' essential part, if part at all,, of the vascular system. 

 Neither Syennesis nor Polybus, who was son-in-law of Hippocrates, so much as mention 

 the heart iji their accounts of the vascular system ; and though Diogenes speaks of it as 

 receiving two large branches, he clearly regards these branches as of no more importance 

 than the branches to other organs or parts (/T. A. iii. 2; iii. 3). A. had therefore to 

 show not only that the heart was the centre of the vascular system, but firstly that it was 

 part at all of that system. 



His arguments are somewhat confusedly given, but may be thus arranged. 



That the heart is part of the vascular system is shown in the first place by dissection ; 

 for, when exposed,- it is seen in most direct and evident communication with the large 

 vessels. Secondly, the heart resembles the rest of the vascular system in structure ; for 

 ' it is hpniogeneous in substance, like the blood-vessels (cf. ii. I^ ■ Note 16). Thirdly, 

 the heart has no nutrient vessels, which can only be explained on the view that it is 

 nourished by blood, of which it .is the receptacle (cf. ii. i. Note 18). The solidarity, 

 of heart and vessels is still further shown by the fact that throbbing occurs sipiultaneously 

 in them all {De Resp. 20, 7). The heart then is part of the vascular system. That it 

 is the centre of the system is shown, firstly, by dissection, for the ■ large vessels seem to 

 radiate from it. Secondly, the heart rs the first 'part formed in the embryo {D. G. ii. 4, 

 33>' 36), and, no sooner is it formed, than it is found -to contain blood, at a time when 

 there are no blood-vessels as yet to be seen (Z><? Resp. 20,' 6) ; that is to say the heart 

 contains blood, at a period when there is no other organ than itself in which the blood 

 can possibly have been fabricated. Thirdly, the seat of fhe blood formation must be 

 some part where there is much heat, and whence heat cannot readily escape. The 

 region of the heart is such ; for the trunk is sensibly hottef than the extremities ; and 

 comparing the heart with th^ rest of the vascular system, its wall, though of similar 

 material, is found to be thicker, so as to keep in the heat. • Fourthly, it is probable, and 

 preferable on practical as well as metaphysical, gi'ounds, that the source of the blood 

 shall be an unpaired and central organ, so as to be in .as equal reach as possible of all 

 parts of the body; and, moreover, seeing of what vital importance such an organ is, 

 that it shall be in some well- protected position. It must also evidently be some part 

 present in all animals that have blood. The heart alone fulfils all these conditions, or 

 fulfils them better than any other organ. Lastly, the heart is shown by independent 

 considerations to be the centre of sensation ; and the intimate relation of sensation with 

 blood-supply renders it highly probable that the sensory centre will also be the blood- 

 centre. M . Edwards. {Lemons sui' la Phys. iii. 5) says that A. was the first to show that 

 'the blood-vessels communicate with tlie heart, or arise from it. It must however be 

 noted that Plato in the Timceus {§ 45) incidentally speaks of the heart as the meeting-point 

 or kilot (fiM^a) of the vessels, and the fountain of the blood. 



6. Cf. Note 10. 



7. Cf. ii. 2, Note 6. 



8. Elsewhere [H. A. iii. 3, 5) A. says that not only some, but all his predecessors held 

 this opinion. ' ' ^ ■ ' . 



9. The temperature of the body sensibly declines, th^ farther one goes from the centre 

 towards the extremities. 



10. The most natural interpretation of this passage and some others would doubtless 

 be that the bipod-vessels pass right through the viscera, and come out again on the other 



