i66 • ■ Notes, ii. 7. . 



as to rival the brains of vertebrates in size and importance. Thus A. , who had made a 

 special study of Cephalopdds, could not help seeing their ganglia, vv'hereas those of 

 other invertebrates are so small that, with his want of instruments, it is no wonder they 

 should have escaped his notice. 



10. Cf. iii. 4, Note 24. . 



11. i.e. the //a mater. A. {H. A. i. i6) describes the brain as having two membranes, 

 an outer and stronger one next to the bone {dura mater), and an inner one in contact 

 with the brain itself (/«■« wa/^r). This latter is the vascular onCj so often mentioned by, 

 Aristotle. This membrane consists in great part of a plexus of extremely numerous and 

 very minute vessels, as A. says. The same statement is to be. found in De Somno, 3, 26 : 

 "The small si^e and narrowness of the vessels on the brain assists in producing' 

 refrigeration and in preventing the easy access of the ascending vapour of nulriment." 

 The real use of the peculiar and extreme subdivision of the arteries before they are 

 distributed to the brain seems to be to make the blood-pressure and blood-supply as 

 uniform and equable as possible in all parts of this sensitive organ. 



12. Not only in the fcetal mammal, but in the adult batrachian and reptile there are 

 special contrivances by which the head is supplied with purer blood than goes to the rest 

 of the body. The anatomical arrangements by which this is brought about were of course 

 quite unknown to A.; but it is not improbable that he may have noticed the different 

 colour of the blood going to the head and of that going elsewhere, in his vivisections of 

 the tortoise {De Resp. 17, 4) and of the chameleon {H. A. ii. 11); . What wasi true of 

 some animals, he supppsed to be true of all, because the conclusion chimed in with his 

 ^/wW views (cf. ii. 2, Note 6). • ■ 



13. The same comparison is to be found in De Somno, ch. 3. 



14r. "As to the causes of health and of disease, these are matters which come not only 

 into the province of the physician, but also to a certain extent into that of the natural 

 philosopher. The two however regard the subject from diiTerent poinjts of view, as must 

 not be forgotten. Still it is plain enough that there is no very broad line of demarcation 

 between them. For such physicians) as are boastful and officious, are given to talk of the 

 phenohiena of nature, and profess to derive from natural philosophy their principles of 

 practice; while the most accomplished among the natural philosophers rarely fail 

 eventually to touch on the principles of the art of healing" {De Long, et £r. Vita, 2). 

 As to the question whether the promised treatise' on the Principles of Disease was ever 

 written, see Heitz, Die verlor. Schrift. d. Arist. p. 58. 



15. A similar account of sleep is given in the special treatise De Somno. A. argues 

 that as the main feature of sleep is the abeyance of all the senses, sleep must clearly be 

 due to some condition of the sensorium commune, i.e. the heart ; and as sleep is notably 

 , consequent on a heavy meal, on severe exercise, and, the like, it must be due to some 

 effect producible by such influences on the heart. After a meal the dissolved food 

 passes into the blood-vessels, as also after severe exercise does the waste matter resulting 

 from such exercise, and ascends through them in form of vapour. When this reaches 

 the head, it is condensed by the cold brain and falls back to the heart as a cold fluid, 

 consistir>g after a meal of the coarse and fine elements of the food, and after exercise of 

 coarse matter only. It is this accumulation of cold; coarse, thick fluid In the sensorium 

 commune that suspends its activity. After a time this fluid undergoes concoction, and 

 then the sensorium is relieved and wakens into activity. What happens in sleep, says A., 

 happens also in an epileptic attack, so that sleep is a kind of epilepsy ; and in confirma- 

 tion of this view he cites, the perfectly accurate facts, that the night is the most usual 

 time for these fits, and that in most cases the earliest attacks occur during sleep. It is 



