DIETETICS. 



which always accompanies fermentation ; 

 this motion is excited by the warmth of 

 that viscus, by the old remnants of the 

 food, by the gastric fluid, and more par- 

 ticularly by the saliva, which is above all 

 adapted to produce and promote this 

 process. They supposed that the first 

 effect of this intestine commotion is to 

 raise the solid parts of the aliment to the 

 surface of the gastric liquor, where they 

 will be for some time sustained by the air 

 bubbles, which, on their ceasing", . must 

 fall down again, and be thoroughly incor- 

 porated with the fluids of the stomach. 

 This mixture is rendered still more com- 

 plete by the peristaltic motion, the alter- 

 nate pressure of the diaphragm and abdo- 

 minal muscles, and the continual pulsa- 

 tion of the adjacent large vessels: in this 

 state the food passes into the small intes- 

 tines, where the fermentative motion pro- 

 duces still greater changes by the assis- 

 tance of the bile and pancreatic juices ; it 

 is then converted into chyle. Accord- 

 ing to the opinion ofHaller, the gastric 

 juice is more or less acid in different ani- 

 tnals ; its action on the food very much 

 resembles that of water, in which a little 

 salt has been dissolved, which, from ex- 

 perience, -is known to possess a very 

 great resolvent power ; and the conse- 

 quence is, that an incipient fermentation 

 takes place, which reduces the aliments 

 to a pultaceous mass. In animals that 

 feed on seeds, this process is assisted by 

 trituration. These, with many other fan- 

 ciful opinions, took place in their turn, 

 when Cheselden by chance happened to 

 conjecture right, viz. that digestion was 

 performed by some unknown menstruum. 

 This conjecture was confirmed by Reau- 

 mur and Spallanzani, who have proved 

 the menstruum to be the gastric juice, 

 by a number of experiments, a general 

 view of which it will be necessary to 

 give. 



Spallanzani made his experiments by 

 introducing certain substances, such as 

 raw vegetables, &c. enclosed in small 

 perforated tubes, and causing animals to 

 swallow them ; he then either destroyed 

 the animal, in order to examine it, or 

 waited until it was vomited up. The 

 animal kingdom may be divided into three 

 kinds; containing stomachs muscular, 

 intermediate, or membranous ; the last 

 class is infinitely more numerous than 

 the two former. Of animals with mus- 

 cular stomachs, such as fowls, turkeys, 

 ducks, geese, doves, pigeons, &c. the 

 food is seeds, such as wheat, barley, 



pease, &c. ; when it is taken spontane- 

 ously by these birds, it remains some 

 time in the craw, where it is macerated 

 and becomes softer; it is then conveyed 

 into the stomach or gizzard, which is 

 composed of very strong muscles, capa- 

 ble of grinding not only the grain it re- 

 ceives, but is of such force as even to re- 

 duce small pieces of glass, and blunt the 

 points of needles : by this means the food 

 is triturated and reduced very small ; it 

 is then converted, by the gastric juice it 

 meets with in this viscus, into a pulta- 

 ceous mass, called chyme. Spallanzani 

 found, that the gastric juice of this class 

 digests flesh, and that the animals are for 

 the most part both frugivorous and gra- 

 nivorous. He found it dissolved raw 

 flesh, when bruised, in about two days ; 

 but when entire, four and sometimes five 

 days were necessary : it dissolves grain 

 only when bruised ; hence, in the gallina- 

 ceous class, trituration and the gastric 

 fluid in the gizzard, although Reaumur 

 was of opinion it contained no menstru- 

 um, mutually assist each other; the 

 former, by breaking down the aliments 

 in a mechanical way, prepares it for the 

 latter, which penetrates it, destroys its 

 texture, dissolves its particles, and dis- 

 poses them to change their nature and 

 become animalized. Spallanzani thinks 

 that this gastric fluid traced in the giz- 

 zard proceeds chiefly from the oesopha- 

 gus; the chyme he found to be a semi- 

 fluid pultaceous mass, of a whitish yellow 

 colour ; the transparency of this gastric 

 juice, in a state of purity, is little inferior 

 to water; it is fluid, and a little bitterish 

 and saline ; it retains, out of the body, 

 when warm, the power of dissolving ani- 

 mal and vegetable substances ; but it 

 must be fresh, for if kept in vessels, par- 

 ticularly if open, it loses its efficacy ; it 

 must nothave been used for experiments; 

 and likewise a heat equal to that of the 

 bird, is necessary, otherwise it has no 

 more effect than water. 



The ruminating animals of the third 

 class, such as sheep, oxen, &c. very much 

 resemble this class of birds in their man- 

 ner of digesting substances: in both, the 

 gastric fluid requires an agent capable of 

 breaking down the food, before it can 

 dissolve it. The hay and grass, in the 

 ruminating tribe, descend immediately 

 into the first and second stomachs, in 

 nearly the same state as when they first 

 brouzed ; here they are softened by the 

 juices, as seeds are in the craws of birds 

 with gizzards; but as the stomachs of 



