160 DIGESTION. 



one after another, by the vessels of the mucous membrane, and 

 carried away by the current of the circulation. 



THE LARGE INTESTINE AND ITS CONTENTS. Throughout the 

 small intestine, as we have just seen, the secretions are intended 

 exclusively or mainly to act upon the food, to liquefy or disinte- 

 grate it, and to prepare it for absorption. But below the situation 

 of the ileo-csecal valve, and throughout the large intestine, the con- 

 tents of the alimentary canal exhibit a different appearance, and 

 are distinct in their color, odor, and consistency. This portion of 

 the intestinal contents, or the feces, are not composed, for the most 

 part, of the undigested remains of the food, but consist principally 

 of animal substances discharged into the intestine by excretion. 

 These substances have not all been fully investigated ; for although 

 they are undoubtedly of great importance in regard to the preser- 

 vation of health, yet the peculiar manner in which they are dis- 

 charged by the mucous membrane and united with each other in 

 the feces has interfered, to a great extent, with a thorough investi- 

 gation of their physiological characters. Those which have been 

 most fully examined are the following : 



Excretine. This was discovered and described by Dr. W. Mar- 

 cet, 1 as the most characteristic ingredient in the contents of the 

 large intestine. It is a slightly alkaline, crystallizable substance, 

 insoluble in water, but soluble in ether and hot alcohol. It crys- 

 tallizes in radiated groups of four-sided prismatic needles. It fuses 

 at 204 K, and burns at a higher temperature. It is non-nitrogen v 

 ous, and consists of carbon, hydrogen, oxygen, and sulphur, in the 

 following proportions : 



C 78 H 73 2 S< 



It is thought to be present mostly in a free state, but partly in union 

 with certain organic acids, as a saline compound. 



Stercorine. This substance was found to be an ingredient of the 

 human feces by Prof. A. Flint, Jr. 2 It is soluble in ether and 

 boiling alcohol, and, like excretine, crystallizes in the form of 

 radiating needles, but fuses at a much lower temperature. It is 

 regarded by its discoverer as produced, by transformation, from 

 cholesterine, one of the ingredients of the bile. 



Beside these substances, the feces contain a certain amount of 



1 American Journal of the Medical Sciences, January, 1855, and January, 1858. 



2 Ibid., October, 1862. 



