348 SECRETION. 



there is an increase in the discharge of urine, with an excretion of sugar due to an exag- 

 geration in the sugar-producing function of the liver. Irritation applied a little higher, 

 toward the pons Varolii and just posterior to the origin of the fifth pair of nerves, is 

 followed by a great increase in the activity of the salivary secretion. 



Mental emotions, pain, and various circumstances, the influence of which upon secre- 

 tion has long been observed, operate through the nervous system. Numerous familiar 

 instances of this kind are quoted in works on physiology: such as the secretion of tears; 

 arrest or production of the salivary secretions ; sudden arrest of the secretion of the 

 mammary glands, from violent emotion ; increase in the secretion of the kidneys or of the 

 intestinal tract, from fear or anxiety ; with other examples which it is unnecessary to 

 enumerate. 



The effects of destruction of the nerves distributed to the parenchyma of some of the 

 glandular organs are very curious and interesting. Miiller and Peipers destroyed the 

 nerves distributed to the kidney and found that, not only was the secretion arrested 

 in the great majority of instances, but the tissue of the kidneys became softened and 

 broken down. These experiments have been repeated by Bernard. He found that ani- 

 mals operated upon in this way died, and that the tissue of the kidney was broken down 

 into a fetid, semifluid mass. After division of the nerves of the salivary glands, the organs 

 became atrophied, bat they did not undergo the peculiar putrefactive change which was 

 observed in the kidneys. The same effect was produced when the nerve was paralyzed by 

 introducing a few drops of a solution of woorara at the origin of the little artery which 

 is distributed to the submaxillary gland. 



General Structure of Secreting Organs. In treating of the mechanism of secretion 

 and excretion, it has been evident that all glandular organs must be supplied with blood 

 to furnish the materials for secretion, and be provided with epithelium, which changes 

 these matters into the characteristic elements of the secretions. We can understand how 

 certain of the liquid and saline constituents of the blood can escape by exosmosis through 

 the homogeneous walls of the capillaries, but the more complex secreted fluids require 

 for their formation a different kind of action ; although, in the act of secretion, there is 

 considerable transudation of liquid and saline matters, which take up in their course the 

 peculiar principles formed by the cells. 



Although it is somewhat difficult to draw a line between transudation and the simplest 

 forms of secretion, it may be assumed, in general terms, that fluids which are exhaled 

 directly from the blood-vessels, without the intervention of glandular apparatus or of a 

 secreting membrane, are transudations ; while all fluids produced by simple membranes 

 or by follicles, or which are discharged from the ducts of glands, are secretions. This 

 division places the intermuscular fluid and the fluid found in all soft tissues among the 

 transudations, and the serous and synovial fluids among the secretions. 



The serous and synovial membranes present the simplest form of a secreting apparatus. 

 Blood is supplied to them in small quantity, and, on their free surfaces, are arranged one 

 or two layers of epithelial ceils which effect the slight changes that take place in the 

 transuded fluids. In some of the serous membranes, as the pleura and peritoneum, the 

 amount of secretion is very small ; but others, like the serous pericardium and the synovial 

 membranes, secrete a considerable quamtity of fluid. The action of all of these membranes 

 may become exaggerated, as a pathological condition, and the amount of their secretions 

 is then very large. 



Anatomists have now a pretty clear idea of the structure of what are called the 

 glandular organs ; and it will be seen that they simply present an arrangement by which 

 the secreting surface is increased, and at the same time compressed, as it were, into a 

 comparatively small space. The mucous follicles, for example, are simple inversions of a 

 portion of the mucous membrane ; while the ordinary racemose glands are nothing more 

 than collections of follicles around the extremities of excretory ducts. These ideas con- 



