I 
CHANGES FOOD UNDERGOES IN THE DIGESTIVE TRACT. 315 
laeces, and lacihtates their evacuation); (6) antiseptic : (Bile is 
said by some to prevent putrefaction ; if true, it must be to a 
l very slight degree, as bacteria thrives in and around it). 
The intestinal secretion is obtained from the glands con¬ 
tained therein, and is a thin, yellowish, alkaline fluid. Speci¬ 
fic giavity i,on. It is capable of converting cane sugar and 
starch into grape sugar, by the action of a special ferment— 
invertin. It brings aboutlactic fermentation, dissolves fibrin 
very slowly ; still less so other proteids. It is also said to 
emulsify fat. 
PUTREFACTIVE FERMENTATION OF THE INTESTINES. 
The lower organisms contained in the air and saliva and 
swallowed, produce certain fermentative changes, quite dis¬ 
tinct from the action of the special ferments of the digestive 
fluids. This is proved by the composition of gases found in 
the intestines. The oxygen of the atmospheric air swallowed 
is absorbed, leaving nitrogen, while a quantity of carbonic 
anhydride and hydrogen from the fermentation of sugar are 
set free. Lactic and butyric-acids are produced at the same 
time. Indol and skatol are formed by putrefactive fermenta¬ 
tion of the leucin and tyrosin. 
A SUMMARY OF DIGESTIVE CHANGES. 
The food when taken into the mouth is, or should be, finely 
subdivided, mixed with saliva, reduced to a pulp, a certain 
amount of starch converted into sugar and rendered alkaline. 
Fats and proteids unaltered. On reaching the stomach the 
mass is rendered acid, conversion of starch into sugar ceases. 
Connective tissue of fats dissolved, fats set free and liquefied bv 
the animal temperature. Proteids dissolved and peptones 
formed. A grumous mixture of peptones, liquid fats, and 
stai ch is formed and called chyme, which on passing into the 
intestines and mixed with the bile, pancreatic and intestinal 
fluids, becomes alkaline. Conversion of starch into sugar re¬ 
commences. Emulsifying and saponifying of fats begin. The 
undissolved proteids are converted into peptones. The diffusi¬ 
ble peptones and salts are absorbed and enter the portal sys¬ 
tem ; the fats in a fine state of subdivision enter the lacteals, 
while the residue or inert material is expelled as fseces. 
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