INTRODUCTION 9 



ample, has identical properties whether derived from the sheep or the 

 whale. A striking feature in case of some of these substances is their 

 high potency. Epinephrin has been shown to exercise a perceptible effect 

 on smooth muscle in dilution of one part in a billion, or about one 

 grain in fifty tons of fluid. The presence of one part in ten millions is 

 easily detected by several of the more delicate biologic methods. An- 

 other striking characteristic of epinephrin is its instability. Even a rela- 

 tively large dose administered intravenously to an animal seems to be 

 quickly destroyed, although Meltzer and Auer have shown that when 

 injected subcutaneously it may cause local vascular changes that persist 

 for hours. If the substance is injected directly into an artery it is so 

 nearly completely removed during its passage through the capillary bed 

 as to exert no demonstrable systemic effect unless relatively very large 

 doses are employed. The thyroid hormone, on the other hand, appears 

 to be relatively stable, continuing to exert its effect, for example, on basal 

 metabolism for days (Plummer). 



The internal secretions proper are to be differentiated from other 

 specific substances found in the blood, such as those involved in the 

 processes of coagulation or in immunity. In some instances the grounds 

 for division are not at all definite. The opsonins, for instance, are "de- 

 rived from cells in one part of the body and influence functions else- 

 where," and thus fall within the conventional definition of hormones. 

 Properly speaking, however, they are not such. Until our knowledge of 

 the chemistry of both immunity and endocrin biology is better estab- 

 lished the classification in such cases must be somewhat arbitrary. 



In considering the active principles of the endocrin glands the fact 

 should not be ignored that the discovery of one such principle in a given 

 organ by no means excludes the possibility of the existence of others. 

 That the suprarenal and pituitary organs produce more than one active 

 substance each is highly probable. The corpus luteum is generally be- 

 lieved to produce a hormone different from any formed by the ovary 

 proper. 



In the therapeutic use of endocrin material these facts should be 

 held in mind. That suprarenal therapy now has questionable standing 

 is possibly due to some extent to a premature conclusion that epinephrin 

 is the active principle rather than an active principle of the gland. Nega- 

 tive results with epinephrin by no means prove that suprarenal treatment 

 is necessarily without value. Unfortunate is the assumption on the 

 part of pharmaceutical manufacturers that any process, which does not 

 destroy a recognized "principle," may safely be used in preparing gland 

 extracts or desiccated gland substances for clinical use. The custom of 

 extracting these materials with fat solvents undoubtedly makes for ele- 

 gance in the finished products but it may also, in some cases, account for 

 the uselessness of the same. 



