CHEMICAL CORRELATION 567 



nutritional condition of a tissue, in the direction either of 

 increased or diminished activity, and that such means are 

 normally employed by the animal body for co-ordinating the 

 activities and growth of widely separated organs. 



Other examples of chemical influences exerted by one 

 organ on other parts of the body are known in which the 

 final effect is not confined to one organ, but is manifested 

 throughout the whole body. In some of these cases the diffuse 

 character of the response is determined by the widespread 

 distribution of some special reacting tissue or function. I need 

 only mention in this connection the important control wielded 

 by such organs as the suprarenals, the thyroid, the pancreas, and 

 the pituitary body on the general metabolic processes of the 

 organism. In the case of the first of these organs, we know that 

 the medullary part secretes a drug-like body, adrenalin, into the 

 blood-stream. This part of the suprarenals is derived in develop- 

 ment from the sympathetic system, and is but one of a series of 

 such organs. The function of its specific product is apparently 

 limited to the sympathetic system. Adrenalin, as Langley and 

 Elliott have shown, acts on every tissue of the body which 

 receives a nerve supply from the sympathetic system, and in 

 every case the effect of its injection is the same as that which 

 would be produced on the tissue by electrical excitation of the 

 sympathetic nerve. Thus it causes dilatation of the pupil, 

 secretion of thick saliva, constriction of the blood-vessels, 

 acceleration of the heart, relaxation of the muscular walls of 

 the small and large intestine, contraction of the ileo-colic 

 sphincter as well as of the uterus, and either contraction or 

 relaxation of the bladder, according to the action of the 

 sympathetic on this viscus, which varies from one species to 

 another. 



In the case of the thyroid gland, it is difficult to say whether its 

 active principle, which is apparently the iodine-containing body, 

 iodothyrin, first prepared by Baumann, is to be regarded as 

 chiefly dissimilatory or assimilatory in its effects. It is certain 

 that its presence in the circulating fluids is a necessary con- 

 dition for the normal development of all the tissues of the body, 

 especially of the bones, in the growing animal, but the effect 

 of its administration to adults is to stimulate dissimilation. It 

 increases the output of urea and may cause a rapid disappearance 

 of fat from the body. 



