SECRETION. 137 



The normal temperature of the body is maintained by a constant expendi- 

 ture of the heat in several directions: 



1. In warming the food, drink, and air that are consumed in twenty-four 

 hours. For this purpose about 157 heat units are required. 



2. In evaporating water from the skin and lungs, 619 heat units being utilized 

 for this purpose. 



3. In radiation and conduction. By these processes the body loses at least 

 fifty per cent, of its heat, or 1,156 heat units. 



4. In the production of work; the work of the circulatory, respiratory, mus- 

 cular, and nervous apparatus being performed by the transformation of 

 369 heat units into units of work. 



SECRETION. 



The process of secretion consists in the separation of materials from 

 the blood which are either to be again utilized to fulfil some special purpose 

 in the economy, or are to be removed from the body as excrementitious 

 matter; in the former case they constitute the secretions, in the latter, the 

 excretions. 



The materials which enter into the composition of the secretions are derived 

 from the nutritive principles of the blood, and require special organs e. g., 

 gastric glands, mammary glands, etc. for their proper elaboration. 



The materials which compose the excretions preexist in the blood, and are 

 the results of the activities of the nutritive process; if retained within the body, 

 they exert a deleterious influence upon the composition of the blood. 



Destruction of a secreting gland abolishes the secretion peculiar to it, and 

 it can not be formed by any other gland; but among the excreting organs 

 there exists a complementary relation, so that if the function of one organ 

 be interfered with, another performs it to a certain extent. 



Classification of the Secretions. 



PERMANENT FLUIDS. 



Serous fluids. Vitreous humor of the eye. 



Synovial fluid. Fluid of the labyrinth of the internal 



Aqueous humor of the eye. ear. 



Cerebro-spinal fluid. 



