244 NUTRITIONAL PHYSIOLOGY 



continually becoming detached and drifting away in the 

 lymph, a phenomenon which is a type of internal secre- 

 tion made visible. They are believed to add substances in 

 solution as well as cells to the passing fluid. 



There is good ground for the view that the lymph- 

 nodes are a defense against the spread of infection. When 

 a boil exists upon the arm the nodes above the place where 

 the bacteria are working so destructively are usually ob- 

 served to be enlarged and tender. The lymph which is 

 returning from the seat of the trouble is bearing the pro- 

 ducts of the suppuration, if not the infecting organisms 

 themselves. Apparently this polluted lymph is more or 

 less successfully disinfected before it is allowed to pass on 

 into the thorax to merge with the blood in the veins. The 

 lymph-nodes of the mesentery stand as outworks of the 

 bodily fortifications against the entrance of microbic 

 invaders from the intestine. When overpowered in their 

 struggle the lymphatic glands themselves become foci of 

 infection, as in the familiar form of tuberculosis known as 

 scrofula. 



One large organ, which from its anatomic relations has 

 been called a ductless gland and which might be expected 

 to have an internal secretion, has failed to give satisfac- 

 tory evidence of such a function. This is the spleen, which 

 is placed below the diaphragm to the left of the stomach. 

 It remains an enigma to physiologists. Its blood-supply 

 is large and its frequent changes of volume, contractions, 

 and dilations alternating in a slow rhythm, give a strong 

 suggestion of some well-marked action in progress. But 

 it has never been shown that an animal is affected in any 

 characteristic way by the loss of the spleen, provided the 

 immediate effects of the severe operation are survived. 

 Certain enzymes have been extracted from the tissue of the 

 spleen, which may have to do with the metabolism of those 

 peculiar proteins which yield uric acid. We may not be 

 warranted in asserting that the spleen has no useful ser- 

 vice to perform, but we can say that other organs appear 

 to be able to make good its deficiency. . 



