THE ELIMINATION OF METABOLIC PRODUCTS. 595 



From the material at hand it is hard to decide as to the significance of the 

 phenomenon, and there is no indication of what substances in the urine 

 exert this poisonous action. In the case of uraemia we have no reason 

 for attributing any one substance as causing the whole complex of 

 symptoms. It is self-evident that all sorts of different substances may 

 come into play here, and furthermore it must never be forgotten that an 

 abnormal composition of the plasma will immediately have an effect upon 

 all the processes of metabolism in the cells, and result in the production 

 of incompletely formed products, or of those which are built up in an 

 unsuitable way. Here, as in all physiological and pathological processes, 

 an organ should not be considered by itself, but we must trace the 

 damages which start from it in a continuous line from organ to organ, 

 from tissue to tissue, and finally from cell to cell. 



The animal organism is also normally eliminating substances constantly 

 through the skin. We find in mammals essentially two kinds of glands 

 in the skin, the sweat-glands and the sebaceous glands. The former 

 eliminate a secretion which consists almost entirely of water. The amount 

 of sweat secreted in the course of a day varies tremendously, and is depend- 

 ent upon certain conditions, and especially upon the demands for a regu- 

 lation of the body temperature. In the evaporation of water from the 

 surface of the body the animal organism finds its most important means 

 for preventing the body from being overheated. A large amount of heat 

 is required to transform water from the liquid to the gaseous state. This 

 causes the body to be cooled. It is interesting to find that the activity of 

 the sweat-glands is influenced by the central nervous system. A secretion 

 may be produced directly by nervous stimulation. 



The sebaceous glands have a different and more local function. Corre- 

 sponding to this fact, their secretion has a quite different composition. 

 In a fresh condition it is an oily, semi-liquid mass, which, on standing in 

 the air, solidifies on the surface of the skin to a greasy tallow. It contains 

 fat, albumin and cholesterol. Its most important function is to lubricate 

 the skin. We will here mention again that a modified sebaceous gland, 

 the oil-bag of birds, contains octadecyl alcohol CisHagO, 1 and finally that 

 the mammary glands likewise may be considered as related to the sebaceous 

 glands. 



1 Rohmann: Hofmeister's Beitr, 6, 110 (1904). 



