CHAPTER VIII 



SECRETION. 



INTERNAL SECRETION. 



THE tissue-activity of the organism may be conveniently classed 

 under three groups : (a) muscular activity, manifesting itself in heat 

 and motion; (b) nervous activity, including all nervous acts, from 

 sensation to reason ; (c) glandular activity, which is the general func- 

 tion of epithelial and lymphoid tissues. It includes all those changes 

 of metabolism whereby there follows, as a result of elaboration, a 

 special mixture. 



It is with the last of the three glandular activity that we are 

 now to deal. However, the human economy being such a complex 

 organism, it must be borne in mind that disturbance or lack of 

 activity of one kind may have a very marked influence upon other 

 metabolic functions. It is well known, especially among animal fan- 

 ciers, what a great effect the removal of the ovaries and testicles 

 may occasion in the development of other organs and in the general 

 nutrition of the body. Proteid waste of increased proportion follows 

 the removal of a considerable portion of renal tissue. The liver is 

 most intimately connected with the metabolism of carbohydrates and 

 proteids as well as those food-constituents which contain iron. 



The gland-cells enjoy an essential role in secretion. These cells 

 are applied upon the basement membrane of the glandular acini in 

 such a fashion that each cul-de-sac is surrounded by a network of 

 capillaries. Ludwig and Tomsa have shown that between the blood- 

 capillaries and the acinus are found lymphatic spaces. The cells of 

 the acinus, surrounded by the lymph in the spaces, take from it the 

 elements needed for the production of their own peculiar secretion. 



Dependent upon the nature of the activity of the epithelium of 

 the glands, the general process of secretion may be said to comprise 

 four distinct modes: 



1. Secretion by Filtration. In this case the glandular epithe- 

 lium does not manufacture any material; it utilizes the principles 

 preexisting in the blood and lymph. This kind of secretion is related 

 to serous transudation,. as of the pleura3 and peritoneum, but it is 

 not a simple filtration. The selective action of the epithelium acts 

 upon the transit of the secretion and varies the proportion of the 



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