PHYSIOLOGY. 



verting into nourishment almost every 

 production of the animal and vegetable 

 kingdoms, so on the other side he may 

 continue strong and healthy although 

 using one, and that a very simple kind of 

 aliment. A woman, whose case is related 

 in the memoirs of the Medical Society of 

 Edinburgh, lived on whey for fifty years. 

 Many men live only on certain vegeta- 

 bles, as potatoes, chesnuts, dates, &c. 

 Some wandering Moors, according to 

 Adamson, live almost entirely on gum 

 Senegal. Fish is the only food of nume- 

 rous uncivilized tribes on different coasts : 

 and flesh of others. Some barbarous 

 hordes still eat raw meat, and even the 

 human body sometimes serves them as a 

 repast. In several islands between the 

 tropics, particularly in the South Sea, 

 there is no fresh water, and the milk of 

 the cocoa-nut is used instead : various 

 other singular facts relating to the food 

 and drink of man, might be collected 

 here, showing very clearly that he is an 

 omnivorous animal. 



Whatever be the diversity of food, the 

 action of our organs always separates the 

 same nutritive principle from it : in fact, 

 let the diet be totally vegetable, or totally 

 animal, the peculiar composition of our 

 organs does not alter, an evident proof 

 that the matter we extract from aliment 

 to appropriate to ourselves, is always 

 alike. 



It has been a matter of dispute, whether 

 pure water furnish any nourishment, or 

 be a mere diluent. 



We have nothing further to say con- 

 cerning the processes of mastication and 

 deglutition, than what the reader will 

 find in the article ANATOMY, under the 

 head of " Organs of Mastication and De- 

 glutition." 



Salivary Secretion. This has been es- 

 timated by Nuck at the quantity of one 

 pint in twenty-four hours. Although it 

 probably goes on, to a certain degree, at 

 all times, yet it is more copious when we 

 take fond; and the augmentation of quan- 

 tity arises partly from stimulus, partly 

 from mechanical pressure. When any 

 acrid matter is taken into the mouth, an 

 increased flow of saliva is produced ; and 

 this may also follow the mere sight of 

 food, and hence has arisen the well-known 

 expression of the " mouth watering." 



All the salivary glands are so situated 

 that the motions of the jaw, and other in- 

 struments of mastication, necessarily sub- 

 jects them to considerable pressure, by 

 which their secretory tubes are evacuat- 

 ed, and new secretion promoted. 



The saliva is conveyed into the nvoulb 

 by the contractile power of the salivary 

 ducts, which, in some rare instances, are 

 said to have projected it even from the 

 cavity of the mouth. The great number 

 of vessels and nerves which belong to, and 

 are placed near these glands, correspond 

 to the copious supplies of fluid which they 

 furnish. 



Besides the simple water furnished by 

 the true salivary glands, the mucous fol- 

 licles, which abound on the surface of the 

 mouth supply a considerable proportion 

 of that fluid, to be mixed with the food. 

 These additions being, by means of mas- 

 tication, intimately blended with the food, 

 not only reduce it to a soft pultaceous 

 mass, more fit for the process of deglu- 

 tition, but also bring it into a state of con- 

 venient preparation for the subsequent 

 process of digestion and assimilation. In 

 this point of view, mastication is very im- 

 portant, as we may observe from the ill 

 effects which ensue when the loss of the 

 teeth renders it imperfect in old persons. 



For the chemical analysis of SALIVA, 

 the reader will look to that word ; and for 

 an account of the digestive process itself, 

 to the article DIETETICS; in which are 

 also several observations respecting food. 



While the dissolution of the food, pro- 

 duced by the solvent action of the gastric 

 juice, is going on, the two orifices of the 

 stomach remain accurately closed. No 

 gas ascends through the oesophagus, ex- 

 cept when the digestive process is imper- 

 fect. Soon the muscular fibres of the or- 

 gan begin to act : the circular ones, con- 

 tracting at first in a vague and oscillatory 

 manner, soon act more uniformly from 

 above downwards, and from right to left ; 

 that is, from the oesophagus to the pylo- 

 rus ; while the longitudinal part approxi- 

 mates the two openings. The pylorus 

 seems to possess a peculiar and exquisite 

 sensibility, by which it distinguishes whe- 

 ther the substances brought in contact 

 with it have been sufficiently acted on by 

 the gastric juice ; if that is the case, it re- 

 leases and allows them to pass, while it 

 remains closely contracted against those 

 which are not thoroughly digested. 



The time occupied by the digestive pro- 

 cess must be expected to vary according 

 to the constitution, age, and health of the 

 individual, and the nature of the aliment ; 

 but it may be stated, in general, at four 

 hours. 



The action of the stomach is sometimes 

 inverted, and the contractions, which in 

 that case are forcible, rapid, and convul- 

 sive, cause vomiting. The exertions of 



