508 OF FOOD, AXD THE DIGESTIVE PROCESS. 



in the nutritive materials, by the admixture of the biliary and pancreatic secre- 

 tions ; and to inquire into the form in which they are received into the absorb- 

 ent vessels. The substances of the first or saccharine group consist chiefly 

 of Sugar and Starch. It appears from the late researches of MM. Bouchardat 

 and Sandras, that Sugar is gradually converted, during its passage along the 

 alimentary canal, into lactic acid ; and that it is absorbed in this form alone, 

 unless it have been administered in considerable quantity or for a long period. 

 The conversion of sugar into lactic acid, appears to be preliminary to the 

 elimination of that substance by the respiAtory process. The particles of 

 Starch, as already mentioned, are but very little acted on by the digestive pro- 

 cess, at least in Man and the Mammalia, unless their envelopes have been 

 previously ruptured by heat or chemical agents ; but the triturating power of 

 the gizzard in granivorous Birds, aided by the high temperature and the more 

 alkaline character of the secretions, enables them to act with more energy upon 

 amylaceous substances. The products of the digestive action upon starch, 

 are dextrine and grape-sugar; and this is gradually converted into lactic acid, 

 in which state it is absorbed. If sugar be introduced into the blood-vessels 

 unchanged, it is drawn off by the urine ; and its heat-sustaining agency, there- 

 fore, is not exerted. It is probably to avoid its too rapid introduction that 

 the conversion of amylaceous into saccharine matter is so slowly effected in 

 the alimentary canal ; this conversion seems to begin in the mouth, to cease 

 in the stomach during the operation of the acid solvent, and to recommence 

 after the neutralization of the acid by the biliary and pancreatic fluids, sub- 

 sequently continuing during nearly the whole of the passage of the alimentary 

 matter along the intestinal tube. It is now quite certain, that the substances 

 of this class may be converted, in the living body, into oleaginous matter. Of 

 the mode and the situation in which this conversion takes place, nothing 

 whatever is certainly known ; but a clue to an acquaintance with the former 

 seems to be given by the recently-discovered fact, that the continued contact 

 of bile with saccharine matter occasions the conversion of a portion of the 

 siigar into an adipose compound ( 835). 



671. The substances forming the Oleaginous class do not seem to undergo 



o 



any change, except minute division of their particles, until the Chyme is min- 

 gled with bile; which substance acts as a soap, and renders the oily matters 

 soluble, or at any rate reduces them to a condition in which they can be ab- 

 sorbed by the lacteals. This, indeed, seems to be the main purpose of that 

 admixture of the bile with the mass in process of digestion, which experiments 

 and pathological observation abundantly prove to be requisite for the due per- 

 formance of that function. Thus, it has been shown by the experiments of 

 Schwann, that, if the bile-duct be divided, and be made to discharge its con- 

 tents externally through a fistulous orifice in the walls of the abdomen, instead 

 of into the intestinal canal, those animals which survive the immediate effects 

 of the operation, subsequently die from inanition, almost as soon as if they 

 had been entirely deprived of food. In like manner, if the flow of the biliary 

 secretion into the intestine be prevented by disease, such as obstruction of 

 the gall-duct, the digestive function is evidently disordered, the peristaltic 

 action of the intestine is not duly performed, the ftrces are while and clayey; 

 and there is an obvious insufficiency in the supply of nutriment prepared for 

 the absorbent vessels. This deficiency seems partly due to the want of power 

 to absorb the oleaginous particles of the food, which is the result of the non- 

 intermixture of the bile with the chyme; and partly to the suspension of the 

 supply of combustible matter, that is afforded by certain constituents of the 

 bile itself, which are destined, not to be carried out of the system, but to be 

 ro-absorbcd. The presence of bile in the stomach has the effect of suspend- 



