LECTURE XXVI. 



THE RELATIONS OF THE ORGANS TO ONE ANOTHER. 



AT the close of the last lecture we referred briefly to the mammary 

 glands. These glands exercise their function only under certain definite 

 conditions. The period of lactation does not begin until about the time 

 the secretion is required by the suckling. Long before the birth, however, 

 external changes may be noticed showing that the glands, then at rest, are 

 developing in such a way that they will be able to meet the demands that 

 are to be laid upon them. We have here an interesting example of the 

 relation of widely different organs to one another. The function of the 

 mammary glands is dependent directly upon the generative apparatus of 

 the female. There must be an intimate connection between the two 

 organs. Just what this is, we cannot 'tell. It is generally assumed that 

 nervous influences cause the coincidence in the development of the preg- 

 nant uterus and that of the mammary glands. It is perfectly conceivable 

 that this assumption is correct, although in recent years it has been shown 

 that many apparently reflex nervous processes may be traced to chemical 

 reactions. We would recall in this connection the influence of the hydro- 

 chloric acid from the stomach upon the secretion of the pancreas. The 

 secretion of the latter is accelerated as soon as the hydrochloric acid enters 

 the intestine. The simplest assumption was that the hydrochloric acid 

 irritated the end-apparatus of the nerves in the intestinal membrane, and 

 thus reflexively stimulated the pancreas into increased activity. It has 

 been shown, however, that the mucous membrane of the intestine contains 

 an antecedent, the prosecretin, which is set free by the hydrochloric acid, 

 and as secretin is carried by the blood-passages into the pancreas. Accord- 

 ing to this, the alimentary tract, or at least that portion which produces 

 the prosecretin, falls into line with those organs which are said to produce 

 internal secretions. It is not right to give a particular position to an organ 

 shown to produce internal secretions. There is no reason why an organ 

 which gives up its secretion directly to the blood should be considered as 

 essentially different from the ordinary glands which send out their secre- 

 tion through ducts. Numerous observations in physiology and in pathology 

 compel us to assume that all the organs are in some way related to one 

 another. We must not be satisfied by merely saying that this connection 

 is made by means of the nerves. It is far more probable that the separate 

 cells of the body not only give up the metabolic end-products to the lymph 

 and blood, but secretions as well. This view seems in accordance with 



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