32 INTERNAL SECRETION 



extracts on the peripheral vessels was employed by Oliver. 

 The vessels of the frog's mesentery were observed before and 

 after the application of a drop of normal saline (as a control) 

 and of normal saline containing 1 per cent, of the organ dried at 

 38 c. the simple saline and the saline extract being exactly 

 of the same temperature (16 C.). Throughout each observa- 

 tion the micrometer scale was kept in situ over exactly the same 

 portion of an artery and its companion vein ; and when any 

 change of calibre was observed to follow the application of the 

 saline extract its duration and degree were noted until the 

 calibre was restored, and it was accepted as the effect of the 

 extract when it exceeded the normal variations and when it was 

 practically immediate, was invariable, and when it lasted a 

 certain uniform time, and was succeeded by restoration of the 

 calibre. There was not much effect except in the case of 

 adrenal extracts. This constricting effect of adrenal extract 

 on the peripheral vessels may likewise be observed by the 

 unaided eye by setting up inflammation of the conjunctiva in a 

 rabbit (as by touching the eyeball with a glass rod dipped in 

 acetic acid) and then dropping the extract on the injected 

 surface, when the redness quickly vanishes, and remains absent 

 for about half an hour. 



But even if, on injection of an extract of an organ, we get 

 several different effects on the organism, it is obvious that we 

 have no right to assume on these grounds alone that the organ 

 yields an " internal secretion." This may be suspected when 

 the extract yields a substance having very special physiological 

 actions, but can be definitely stated only when the organ con- 

 sists of glandular " secreting " cells which show histological 

 signs of activity (granules, etc.), and when the blood which 

 leaves the organs by its veins can be found to contain the same 

 active principle as the organ itself. To make the evidence for 

 internal secretion complete, it ought to be possible to recognize 

 in the symptoms produced by extirpation of the organ the 

 direct and reasonable effects of absence of the active principle, 

 the internal secretion, and to remove these symptoms by re- 

 placing the organ in some other part of the body or by admin- 

 istering the active principle in some form or other. 



Isolated organs and tissues are now employed frequently in 

 nnlrr to tr-t the effects upon them of extracts of the various 

 organs. Thus a strip of uterine wall or of different portions of 



