SECRETION. 313 



fibrous tumors, organic muscular fibres, found in a very ill- 

 developed condition in its quiescent state, are then enormously 

 developed, and provide for the expulsion of the foetus or- the 

 foreign body. Other examples of the same kind are furnished 

 by cases in which, from obstruction to the discharge of their 

 contents and a consequently increased necessity for propulsive 

 power, the coats of reservoirs and of ducts become the seat 

 of development of organic muscular fibres, which could be 

 said only just to exist in them before, or were present in a 

 very imperfectly developed condition. 



Respecting the mode and conditions of the process of growth, 

 it need only be said, that its mode seems to differ only in de- 

 gree from that of common maintenance of a part ; more par- 

 ticles are removed from, and many more added to a growing 

 tissue, than to one which only maintains itself. But so far 

 as can be ascertained, the mode of removal, the disposition of 

 the removed parts, and the insertion of the new particles, are 

 as in simple maintenance. 



The conditions also of growth are the same as those of com- 

 mon nutrition, and are equally or more necessary to its occur- 

 rence. When they are very favorable or in excess, growth 

 may occur in the place of common nutrition. Thus hair may 

 grow profusely in the neighborhood of old ulcers, in consequence, 

 apparently, of the excessive supply of blood to the hair-bulbs 

 and pulps ; bones may increase in length when disease brings 

 much blood to them ; and cocks' spurs transplanted from their 

 legs into their combs grow to an unnatural length ; the conditions 

 common to all these cases being both an increased supply of 

 blood, and the capability, on the part of the growing tissue, of 

 availing itself of the opportunity of increased absorption and 

 nutrition thus afforded to it. In the absence of the last-named 

 condition, increased supply of blood will not lead to increased 

 nutrition. 



CHAPTER XII. 



SECRETION. 



SECRETION is the process by which materials are separated 

 from the blood, and from the organs in which they are formed, 

 for the purpose either of serving some ulterior office in the 

 economy, or being discharged from the body as excrement. In 

 the former case, both the separated materials and the processes 



