Notes, ii. 3. I59 



2. Bile obtained from the gall-bladder is usually very viscid, owing to the admixture 

 of mucus, derived from the walls of that receptacle, with the slightly alkaline fluid. 

 When* this viscid bile is left to stand, the mucus rapidly decomposes, and the fluid 

 becomes acid. This disappearance of the mucus restores to the bile the greater degree 

 of fluidity, which it had before entering the gall-bladder. 



3. The opinion that digestion is due to heat appears to have origitiated with 

 Hippocrates, and was adopted by A. and also by Galen. Digestion according to this 

 view was a process of cooking (see however ii. 6, Note 7), and in Greek the same word 

 (ire'ifjs) stands for both cooking and digestion. Our words "dyspepsia" and "pepsine" 

 are records of the old. belief, which was prevalent for ages after A.'s time, the action 

 of the heat being still called "concoction." The various opinions as to the cause of 

 digestion are thus enumerated by Celsus : " Duce, alii, Erasistrato atteri cibum in ventre 

 contendunt ; alii, Pleistonico Praxagorse discipulo, piitrescere ; alii credunt Hippocrati, 

 per calorem cibos concoqui ; acceduntque Asclepiadis aemuli qui omnia ista vana fet 

 supervacua proponunt ; nihil enim concoqui, sed crudam materiam, sicut assumpta est, 

 in corpus omne diduci." Although we have now learnt that digestion is due to the 

 action of gastric and other juices, yet it is- no less certain that heat is not without 

 considerable influence on the process, A temperature of from 106° to 96° F. is in fact 

 necessary in order to keep up the chemical process, and each successive fall below 

 this standard produces successive retardations of the action ; which is completely 

 suspended when the ordinary atmospheric temperature is reached. On the other hand 

 a rise of temperature to about "140" F. causes a decomposition of the gastric juice, and 

 entirely destroys its power. 



4. A. looked on the heart as the main but not the exclusive seat of vital heat. "The 

 whole body and all its parts have a certain innate natural heat. But in sanguineous 

 animals the main seat of this heat must be- the heart. For, though the other parts by their 

 natural heat ,can effect the concoction of the food, yet chief and foremost in this office 

 is the heart. The rest of the body then may become cold, and yet life continue ; but 

 should the heart cease to be hot, all life is at an end ; for no longer does there remain 

 a source whence the rest of the body may derive heat " {De yuv. et Sen. 4, 3). 



6. A. knew nothing of the salivary glands, or of their action upon starch. He 

 therefore limits the part played by the mouth to mastication, which he truly says is not 

 actually a digestive process, though essential for easy digestion. 



6. The upper cavity is of course the stomach. By the lower is meant the large 

 intestine, or rather its csecal enlargement (cf. iii. 14, Note 35). This is sometimes, as 

 here, spoken of by A. ds a seat of digestion, that is as a second stomach, and sometimes 

 merely as a receptacle of residual matter, as though all digestion were over before this 

 part was reached. We may fairly suppose that A. in the different passages is speaking 

 of different animals ; for while the caecum in sOme animals, as in the horse, really acts 

 as a second stomach, in others, as in man, its contents are almost entirely faecal. 



7. The same simile occurs in the Timseus {Jinveti's Tr. ii. 564). 



8. One term (ircptTTcojuo) served A. to express several things, viz. (i) The indigestible 

 residue of food, i.e. the excreta. This is often distinguished as the "useless residuum" 

 ^i. 10, 2 ; Z>. G. i. 18, 2). (2) Such part of the food as, though nutritious, is not 

 consumed for the direct benefit of the individual, but for that of the species, as milk, 

 semen, and generally the generative secretions (iv. 10, 47). (3) The parts of the 

 blood which remain after the nobler organs have been supplied, and which are used 

 for the inferior parts, such as sinews, bones, etc. (iii. 5, Note 5). (4) Such inferior 

 parts themselves, e.g. hairs (ii. 15, Note 4). (s) Such surplus materials as are not used 



