164 ■ Notes, ii. 6. . ■ 



(Ch. 6.) 1. Alluding to Plato, who expresses this view in the Timseus {JoTvelfs 

 Transl. ii. 571). 



2. "The bones of the foetus are void of a distinct medullary canal, and present 

 merely a reddish homogeneous vascular pulp, somewhat consistent but presenting soft 

 portions. This state continues for some time after birth" {Todd's Cyclop. Anat. i. 60). 

 So also VirchoTv's Cellularpath. 369, 



3. In the foetus and infant there' is less pigment in the body generally than in the adult. 

 The skin, hair, eye's (Z?. G. v. i, 16), and olfactory region, are all lighter-coloured than 

 in later life. I have tried to show elsewhere {Med. Chir. Trans. 1870) that this develop- 

 ment of pigment after birth coincides with, and is a necessary condition of, an increased 

 sensory acuteness. 



4. That the spinal cord is the marrow of the vertebrae is an error, the memory of which 

 is still preserved in the popular term "spinal marrow." Although A. observed that the 

 cord was in substance quite iinlike any other marrow, having indeed no other resem- 

 blances to this substa^ice, than its position in a bone cavity and its Hght colour, and 

 though he knew that it was directly continuous with .the brain, which latter he 

 knew was not marrow (see next chapter), yet he held fast to the popular notion, 

 because his theory required the cord to be made of some hot substance, such as he took 

 fat to be. The uses assigned by A. to the spinal cord were, firstly, the mechanical 

 office of holding the vertebrae together, and, secondly, that of tempering the heat of 

 the brain. 



•5. Cf. H. A. iii. 7, 9 : "Sgme animals, the lion for instance, appear to have no mar- 

 row in their bones, because the marrow is excessively small and only present in a few of 

 the bones, as in those of the thighs and fore-legs." "Whether the lion (iv. 10, Note 6) has 

 or has not smaller medullary cavities than weaker animals, I cannot say ; but it would 

 appear to have bones of more than ordinary density. For the per-centage of hard matter in 

 its bones is 72*3, that of man 68-9, of the ox 69, of the porpoise (i\'\ (Oweii's Verteb. i. 

 20). So hard are the lion's bones, says Aristotle (ii. <^ ; H. A. iii. 7, 9), that they give 

 out sparks when struck. ^ 



6. A. distinguishes the substance of which fish-bones are made from that which 

 composes ordinary bone. The difference consists in there being a much srftaller amount 

 of heavy inorganic matter in the former than in the latter. . It may fairly be supposed 

 that this is of use to the fish by diminishing the specific gravity of its body ; and it is in 

 harmony with this view that»thfe proportion of inorganic matter is much higher in the bones 

 of sea-fishes than of such as live in fresh water, the former swimming in a denser medium. 

 The porpoise, though a mammal, has bones iri this respect- like those of a sea-fish (Owen's 

 Verteb. i. 20) ; and as A. in this place speaks not merely of fishes, but of aquatic animals 

 generally, we might suppose him to mean to include this animal, were it not that 

 elsewhere (ii. 9, 11, and H. A. iii. 7, 9) he expressly says, as others had sai'd before 

 Jiim {Herod, iv. 53), that the dolphin has true bones, and not fish-spines. 



7. This passage is of importance ; for it indicates the answer to the obvious objection, 

 that many of the phenomena attributed by A. to heat are manifestly not so producible. 

 For, in using the term "self-concoction," A. means to draw a distinction between 

 ordinary heat, and the heat of the blood or body. Mere cooking with fire of course does 

 nof convert blood into fat, nor digest food, nor the like. But the heat of the body, as 

 the heat of the sun, says A. {D. G. ii. 3, 13), is something very different from this. . It 

 has a vivifying influence, which simple fire has not, and produces effects far beyond the 

 power of this element. Cf. Introd. p. xxiii. 



8. No fish has a medullary canal in its bones, though there are some, as the trout, in 



