DEFINITION OF THE TERM ' INTERNAL SECRETION ' 7 



described, either genetically or morphologically, as epithelial or 

 glandular tissue. If, in considering the activity of the true glands 

 whether ductless or otherwise we are prepared to recognize 

 one secretion only, and to describe it as internal or external 

 according to the direction in which it is discharged, then we are 

 compelled to regard all glands as having more than one secretory 

 surface, and should need proof, moreover, that both internal and 

 external secretion are elaborated by the same morphological ele- 

 ments. But it will be obvious, from what has gone before, that 

 such a theory cannot be made to include all the facts. For 

 instance, it is very possible that, in the case of the male sexual 

 glands, the internal secretion is not elaborated from the 

 spermatozoa-producing elements, but from the interstitial tissues. 



Looking at the matter from the physiological point of view, 

 we must assume that all organs, in addition to their special 

 function which is determined by their structure, possess a specific 

 productive activity, otherwise an internal secretion, which is 

 largely independent of structure. The description " internal secre- 

 tion " is hardly to be improved upon. It expresses the idea which 

 has animated the doctrine from its earliest inception, namely, 

 that the specific internal secretions are physiological hormones 

 affecting the activity of other parts of the body and affecting the 

 body as a whole, and that they are the means by which the 

 chemical correlations of the different organs are brought about. 



There is a large group of chemical adjustments which cannot 

 be included among the internal secretions. It comprises all those 

 readjustments which take place when drugs or poisons are intro- 

 duced into the economy. During the last decades, investigation 

 has revealed a not inconsiderable group of chemical interactivities 

 which are aroused in the body for purposes of offence and defence, 

 not only by the causes of disease, but by poisons of all sorts. 

 There is no doubt whatever that the processes by which anti- 

 toxins and antibodies are formed, are the outcome of a modifica- 

 tion of the chemical activity of the tissues, and that the most 

 important part is played by the internal secretion of the cells. It 

 is, however, expedient to the present purpose to confine the dis- 

 cussion solely to those chemical correlationships which are 

 maintained between the different parts of the body without the 

 intervention of external agents. 



Nevertheless, it is not possible, in the nature of things, to keep 

 entirely within these limits, seeing that no organism lives for itself 

 alone, but is in constant relationship with its surroundings. 

 Foreign materials are introduced into the economy by means of 

 foodstuffs; in the intestinal canal they become so changed by the 

 flora and the ferments that poisonous products of decomposition 

 are formed, and these find their way into the blood-stream. The 

 intermediary toxic substances formed from the splitting up of the 

 foodstuffs, especially of albumen, are rendered innocuous by the 



