384 USES OF THE LIVER DUCTLESS GLANDS 



intestine ; but these phenomena occurring after removal of one kidney 

 are not so readily explained. 



Cases are on record of congenital absence of the spleen in the 

 human subject, in which no special phenomena had been observed dur- 

 ing life. 



Aside from certain uses connected with changes in its volume, it is 

 certain that the spleen has an important relation to the development of 

 blood-corpuscles, both white and red. In certain cases of leucocythe- 

 mia, the spleen is in a condition of hyperplastic enlargement. The 

 blood coming from the spleen is peculiarly rich in leucocytes, but the 

 proportion of its red corpuscles is diminished. It may be that the spleen 

 destroys a certain number of red corpuscles, the coloring matter being 

 changed into other pigmentary matters, and that it also produces new 

 red corpuscles. After removal of the spleen, the red blood-corpuscles 

 are diminished in number and the proportion of leucocytes is increased. 

 This condition continues for about six months ; but after that time, in 

 dogs, the marrow of the long bones, which normally is yellow, becomes 

 red, assuming the character of the marrow concerned in the formation 

 of blood-corpuscles. Temporary diminution of red corpuscles and 

 increase of leucocytes have been observed in the blood in cases of 

 extirpation of the spleen in the human subject. Whatever uses the 

 spleen has in connection with the development of red and of white 

 blood-corpuscles it shares with the red marrow of the bones and the 

 so-called lymphatic glands. 



A theory has been proposed that the cells of the Malpighian bodies 

 of the spleen act as phagocytes and destroy certain pathogenic bac- 

 teria (Metschnikoff). This notion was based on experiments on mon- 

 keys with the spirillum of relapsing fever ; but the original observations 

 were not fully confirmed by other investigators. As the result of care- 

 ful experiments on rabbits, Melkinow-Raswedenkow drew the conclu- 

 sion that while removal of the spleen diminishes the power of resistance 

 to certain infections, the structures in this organ do not act as phagocytes 

 and destroy micro-organisms. This question, however, belongs to pathol- 

 ogy rather than to physiology. 



The production, in the spleen, of a kinase, which converts trypsin- 

 ogen into trypsin, has already been mentioned in connection with the 

 pancreatic secretion. 



THYROID GLAND 



The thyroid gland is attached to the lower part of the larynx and 

 follows it in its movements. Its color is brownish red. The anterior 

 face is convex and is covered by certain of the muscles of the neck. 



