DIGESTION. 201 



The Nerve Mechanism of the Large Intestine. The nerve mechan- 

 ism of the large intestine includes both motor and inhibitor nerves. The 

 motor nerves comprise both pre- and postganglionic fibers; the former 

 have their origin in the spinal cord, from which they emerge in the third and 

 fourth sacral nerves and pass by way of the pelvic nerve to the pelvic 

 ganglia around the cells of which their fibers arborize; the latter (post- 

 ganglionic) fibers emerge from the cells of these ganglia and are distributed 

 to circular and longitudinal muscle-fibers of the intestinal wall. 



The inhibitor fibers also comprise both pre- and postganglionic fibers; 

 the former have their origin in the lumbar region of the spinal cord, from 

 which they emerge in the second to the fifth lumbar nerves; they then pass into 

 and through the sympathetic chain and the inferior splanchnic nerves to the 

 inferior mesenteric ganglion around the cells of which they arborize; the 

 postganglionic fibers pass directly to the muscle-fibers of the intestinal wall. 

 Stimulation of the pelvic nerve with induced electric currents causes con- 

 traction of the muscle-fibers; stimulation of the hypogastric nerves causes 

 an inhibition of the contraction. 



Intestinal Fermentation. Owing to the favorable conditions in the 

 intestine for fermentative and putrefactive processes e.g., heat, moisture, 

 oxygen, and the presence of various microorganisms the food, when con- 

 sumed in excessive quantity or when acted on by defective secretions, under- 

 goes a series of decomposition changes which are attended by the production 

 of gases and various chemic compounds. Dextrose and maltose are partially 

 reduced to lactic acid; this to butyric acid, carbon dioxid, and hydrogen. 

 Fats are reduced to glycerol and fat acids, the glycerol, according to the 

 organisms present, yields succinic acid, carbon dioxid, and hydrogen. The 

 proteins under the prolonged action of the erepsin of the intestinal juice are 

 reduced, with the production of leucin and tyrosin. These crystalline 

 compounds are in turn reduced to simpler forms. The former yields valer- 

 ianic acid, ammonia, and carbon dioxid; the latter, tyrosin, gives rise to indol, 

 which is the antecedent of indican, found in the urine. This compound is 

 discharged in part in the feces though it is in part absorbed into the portal 

 blood and carried direct to the liver where it is oxidized to indoxyl and com- 

 bined or conjugated with potassium sulphate forming the salt potassium 

 indoxyl sulphate or indican, after which it enters the blood, is carried to and 

 eliminated by the kidneys. The presence of this salt in the urine can be 

 demonstrated by adding hydrochloric acid with a small quantity of potassium 

 chlorate; after this is done the indican combines with water and under- 

 goes a cleavage into indoxyl and potassium sulphate; the former then 

 combines with oxygen and gives rise to indigo blue. The extent to which 

 the indican is present is taken as a measure of the extent of intestinal 

 putrefaction. 



Skatol, another derivative of the protein molecule, the result of bacterial 

 decomposition, passes in part into the feces and gives to them the character- 

 istic odor. It is also in part absorbed and oxidized to skatoxyl, after which 

 it combines with potassium sulphate to form potassium skatoxyl sulphate. 

 It is eliminated in the urine by the kidneys. 



The Feces. The feces is a term applied to the mass of material ejected 

 from the rectum through the anus. They are characterized by consistency, 



