OF THE SECRETIONS IN GENERAL. 289 



the example of many of our fluids, which, although 

 secreted by organs at first sight very different from 

 each other, have considerable resemblance to each 

 other in nature; v. c. the saliva and gastric juice. And 

 comparative anatomy teaches us, that the same fluids 

 are formed by organs very different in external appear- 

 ance, in different animals.* (C) 



474. We shall now investigate the causes why par- 

 ticular fluids are found in particular organs, — the most 

 difficult part of the doctrine of secretion, and still open 

 to many doubts. 



475. There can be no question that the absolute 

 cause of the variety of secretions is referrible to the 

 intimate nature of the secreting organ. This depends, 

 in the conglomerate glands and secreting viscera espe- 

 cially, both upon the direction and distribution of the 

 secreting blood-vessels, and upon the peculiar paren- 

 chyma of each secreting organ, in some instances dis- 

 tinguishable at first sight from the substance of every 

 other part. (20) 



476. It is likewise probable, and indisputable argu- 

 ments in favour of the opinion have been continually 

 afforded in the course of this work, that secreting 

 organs have not only a peculiar parenchyma, but a 

 vita propria — a peculiar species of vitality distinct 

 from the common vital powers of contractility, irrita- 

 bility, and sensibility. (D) 



477. The absorbent system seems of much import- 



* Compare, for instance, the form of the kidneys in mammalia with the 

 true conglomerate glands which supply their place in birds ; or the pancreas of 

 warm-blooded animals with the pyloric appendices which, although varying 

 in appearance in different fish, secrete a fluid very similar to the pancreatic. 



U 



