22 INTERNAL SECRETION 



teristic increase in blood-pressure, while in the case of others 

 the effect is to reduce blood-pressure. These changes of tension 

 form the basis for a classification of the internal secretory organs 

 into " hypertensive " and " hypotensive " (Livon). 



But it must be remembered, and the warning will be repeated 

 when we are dealing with the organs separately, the effect of an 

 organic extract in changing blood-pressure is not a proof that 

 the internal secretion of the organ is active in the same way. 

 An organic extract is a mixture of substances, the chemical 

 properties of which are by no means clearly defined. Moreover, 

 the effects which we are able to observe are not necessarily due 

 to the activity of a single substance specific to a single organ ; 

 but may result from the activity of one or more substances, which 

 may be common to many organs. Thus, the depressing action 

 of many organic extracts may be due to the fact that they contain 

 choline, which, it is known, reduces blood-pressure. In addition 

 it may be remarked that changes in blood-pressure may also be 

 caused by intra-vascular coagulation. 



It is obvious, from what has been said, that conclusions as 

 to the physiological and haemodynamic activities of any organic 

 extract, should be accepted only with the greatest caution. Well- 

 defined results must be obtained and an exact knowledge of the 

 chemical characterization of the active substance is essential. But 

 even where these requirements are fulfilled, there must be definite 

 proof that the active substance is formed intravitally, and that 

 it does pass into the blood-stream. Then, and then only, are 

 we in a position to state, that the substance in question is the 

 product of the internal activity of a certain organ. This con- 

 clusion will be confirmed by the morphological proof of secretory 

 cells in the organ in question, and by the histological evidence 

 of the different stages of secretory activity. 



The physiological activity of the organic extracts is not 

 confined to the circulatory system, but may show itself in modifi- 

 cation of the function of other organs. A closer investigation 

 of their effects shows that many organic extracts contain substances 

 which exercise a specific influence upon the nervous system, the 

 muscular structure, the glandular cells, &c., and which affect the 

 general metabolic processes in a special manner. In cases where 

 this influence is extended to functions which are modified inversely 

 by suppression of the organ, there are eminently rational ground* 

 for a substitution therapy. 



Naturally, many of the physiological effects of the organic 

 extracts upon certain tissues are to be observed only after pro- 

 longed use. They sometimes take the form of structural 

 alteration. 



The material which has been collected during the last two 

 decades has materially altered the point of view with regard to 

 the interrelation of the bodily parts. Twenty years ago, the 



