THE DUCTLESS GLANDS. 211 



This view of the action of the liver appears also to "be sustained by the 

 large number of star-like and corrugated blood-cells occurring in the 

 pgrtal blood of fasting animals, and which are replaced by such as appear 

 to be young and perfect in the blood of the hepatic veins. It is not, 

 however, to be supposed that all the iron is economized in this manner ; 

 a considerable portion of it accompanies the pigment as an essential in- 

 gredient, and is finally discharged through the intestine. 



OF THE DUCTLESS GLAOT)S. 



The salivary and sudoriparous glands discharge their secretion directly 

 through ducts. The liver and kidneys have upon their ducts The ductless 

 an additional mechanism, the gall bladder in the one case, and glands. 

 the urinary in the other, which serve as receptacles for storing up the 

 product of action in a temporary manner, and so converting the continu- 

 ous effect of the gland into a periodical result. In each of these instances 

 we may arrive at conclusions of a certain degree of exactness respecting 

 the functions and use of the gland from a study of the secretion it yields ; 

 but there are in the system other glandular organs which differ essen- 

 tially from all the preceding in not being furnished with ducts. These 

 are the spleen, the thymus and thyroid glands, and the supra-renal cap- 

 sules. 



Much diversity of opinion prevails respecting the true nature and ac- 

 tion of these bodies. From their structure bearing a resent Their supposed 

 blance to that of the preceding, with the exception of the ab- functions, 

 sence of a duct, many have thought that, like them, they are really secret- 

 ing organs. Others have supposed that they have a relation to the nu- 

 trition of the system, in giving origin to the development of cells, or that 

 they are connected with the organization of the blood itself; and that 

 such is their duty is perhaps rendered probable by the circumstance that 

 some of them, as the thymus and thyroid, exhibit their utmost develop-, 

 ment when the body is rapidly growing, and diminish when maturity is 

 reached. That they enjoy a community of action, or that their function 

 can be vicariously discharged by other organs, has been clearly estab- 

 lished by the result of operations in which one or other of them has been 

 extirpated. 



With respect to the spleen, the views of Professor Kolliker are sup- 

 ported by many facts. He supposes that one of the chief func- Function of 

 tions of that gland is the dissolution of the disorganizing blood- the s P leen - 

 cells preparatory to the action of the liver, in which ha3matin is to be 

 converted into the coloring matter of the bile. In the discussion entered 

 into respecting the origin of the bile, we have come to the conclusion 

 that it is derived from the systemic venous blood, and in the supposition 

 here presented respecting the function of the spleen there is nothing con- 



