386 HUMAN PHYSIOLOGY 



definitely supported the natural assumption. The spleen 

 has a large blood-supply and is periodically contracted 

 and enlarged as though it were actively engaged in some 

 way. But it has been found that animals and men sur- 

 vive its removal, provided they rally from the immedi- 

 ate effects of the operation. Obscure differences in the 

 composition of the blood have been noted in such surviv- 

 ing animals, and we have previously said that there is 

 sometimes a lessened destruction of the red corpuscles. 



The Thymus. This is an organ below the thyroid and 

 behind the upper part of the breast bone. It is very large 

 in embryonic life and through infancy, gradually dimin- 

 ishing later until only scattered remnants of its tissue 

 are left. It is the " neck sweetbread " of the market. It 

 is probable that the thymus has some regulating effect 

 in the processes of growth and development. The same 

 has been claimed for the pineal body, an outgrowth from 

 the dorsal surface of the brain-stem. 



Attention has been called recently to the similarity 

 between the effects produced by feeding the substance of 

 several organs of internal secretion and the influence of 

 the bodies we have called vitamins. The hormones from 

 the thyroid, the thymus, the hypophysis, and the pineal 

 body may enter into the nutrition of various tissues in much 

 the same helpful way as these accessory compounds in 

 the diet. The suggestion has also been made that the 

 vitamins are particularly useful to the glands of internal 

 secretion. These organs may transform the vitamins of 

 the food into hormones needed by the tissues. 



There is an aspect of this subject which, in the present 

 state of our knowledge, adds greatly to its difficulty and 

 obscurity. This is the circumstance that the organs of 

 internal secretion have reciprocal relations of extreme 

 complexity. One hormone may be auxiliary to another 

 or it may be antagonistic. The future treatment of the 

 matter will be shaped in conformity with a vast number of 

 facts of this kind and its trend can hardly be foreseen. 



