70 HUMAN PHYSIOLOGY. 



organs, <?. ., 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 cannot 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. 



TRANSITORY FLUIDS. 



Mucus. Gastric juice. 



Sebaceous matter. Pancreatic juice. 



Cerumen (external meatus). Secretion from Brunner's glands. 



Meibomian fluid. Secretion from Leiberkiihn's glands. 



Milk and colostrum. Secretions from follicles of the large 



Tears. intestine. 



Saliva. Bile (also an excretion). 



EXCRETIONS. 



Perspiration and the secretion of Urine. 



the axillary glands. Bile (also a secretion). 



FLUIDS CONTAINING FORMED ANATOMICAL ELEMENTS. 



Seminal fluid, containing spermatozoids. Fluid of the Graafian follicles. 



The essential apparatus for secretion is a delicate, homogeneous, 

 structureless membrane, on one side of which, in close contact, is a capil- 

 lary plexus of blood vessels, and on the other side a layer of cells whose 

 physiological function varies in different situations. 



Secreting organs may be divided into membranes and glands. 



Serous membranes usually exist as closed sacs, the inner surface of which 

 is covered by pale, nucleated epithelium, containing a small amount of 

 secretion. 



