332 THE HUMAN BODY. 



they can only go forwards, that is, towards the ending of 

 the duct in the veins of the neck. 



During digestion, moreover, the contraction of the villi 

 will press on the lymph or chyle; and in certain parts of the 

 Body gravity, of course, aids the flow, though it will impede 

 it in others. 



The Spleen. There are in the Body several organs of 

 such considerable size, and of so great constancy in a large 

 number of vertebrate animals, that they would a priori 

 appear to be of considerable functional importance. What 

 their use may be is still, however, unknown or uncertain. 

 They are commonly spoken of collectively, along with the- 

 lymphatic ganglia, as the ductless gland*; but they are not 

 glands in the proper sense of the word. The spleen is the 

 largest of them. It is a red organ situated at the left end. 

 of the stomach (Fig. 103)* and about 17C grams (6 oz.) in 

 weight. Its size is however very variable; it enlarges during: 

 digestion and shrinks again after it until the next meai. In 

 malarial diseases it also becomes enlarged, frequently to a 

 very great extent, and then constitutes the so-called "ague- 

 cake." In structure, the spleen consists of a connective- 

 tissue capsule, rich in elastic fibres, and giving off processe. 

 which ramify through the organ and form a framework for 

 its pulp. The latter contains numerous blood corpuscles; 

 and many bodies which seem to be red corpuscles in pro- 

 cess of decay or destruction. Hence the spleen has been 

 supposed to be a sort of graveyard for their bodies a place 

 where they are broken up and their materials utilized when 

 they have run their life cycle. Others, however, consider 

 that in the spleen new red blood corpuscles are pro- 

 duced from colorless; and others, again, that the main 

 function of the organ is the formation of substances which 

 are carried off to the stomach and pancreas, to be there 

 finally elaborated into digestive ferments. The arteries 

 of the spleen open directly into the pulp cavities, from 

 which the veins arise. On their walls are rounded whitish 

 nodules about the size of a millet-seed, and known as the^ 



* P. 327T~ 



