DIGESTION. 53 



the acids of the stomach, with which they form definite chemical 

 compounds. 



Tlie quantity of gastric juice prepared, is regulated by the wants 

 of the systejn^ and not by the amount of food taken; hence all that 

 is taken over and above these wants will act as a source of irritation. 

 All substances are not equally soluble in the juices of the stomach; 

 in general terms it may be said, that animal food is more soluble than 

 vegetable, though there are exceptions to this rule. Of the saccharine 

 growp^ sugar is generally converted into /ac^ic«czc/ during its passage 

 along the intestinal tube, and is probably absorbed in this form unless 

 it have been administered for a long time. The particles of starch, 

 when their envelopes have been ruptured, are converted into dex- 

 trine and grape sugar ; and this is gradually converted into lactic 

 acid, in which state it is absorbed. It is now certain that the sub- 

 stances of this class may be converted into oleaginous compounds, 

 though the mode and situation in which this change occurs is not cer- 

 tainly known; probably it is by the action of the bile, the long-con- 

 tinued contact of which with saccharine matter occasions the conver- 

 sion of part of it into an adipose compound. 



The substances of the oleaginous class do not undergo much 

 change in the stomach, except a minute subdivision of their particles 

 in the form of an emulsion. When the bile is mixed with them they 

 form a saponaceous compound which is more readily absorbed by 

 the chyliferous vessels. 



The albuminous and gelatinous articles undergo no other change 

 than one of simple solution. 



Lastly, the bolus is exposed to the temperature of the stomach, 

 which is about 100° Fahr. It was found by the'experiments of Dr. 

 Beaumont that the gastric juice had very little effect in dissolving 

 alimentary matters, when the temperature was below this. Hence 

 the taking of cold drinks during digestion is extremely prejudicial to 

 this act. 



The fluids taken into the stomach are for the most part absorbed 

 from it, and do not even pass the pylorus. The solids, with the 

 exception of the insoluble parts, are reduced to a substance called 

 chyme, the consistence of which will of course vary with the amount 

 of fluids taken. In general it is grayish, semifluid, and homogeneous, 

 with a slightly acid taste and smell. When the food has been of a 

 rich character it resembles cream; when of a farinaceous order, it 

 resembles thin gruel. 



The time occupied in the reduction varies, according to the nature 

 of the food, from three to five hours ; and it is now generally con- 

 ceded that this reduction is a true chemical solution, and not a pro- 

 cess o? putrefaction, trituration, ov fermentation. 



The gas contained in the stomach during digestion is generally 

 very small in quantity. Magendie and Chevreul obtained some from 



5* 



