DEFINITION OF " INTERNAL SECRETION " 19 



be due to the influence of embryonic tissue formed by the 

 tumour. 



The object of the present chapter has been to define as 

 accurately as possible what we mean by internal secretion. 

 The point of greatest importance is to limit our conception 

 of internal secretion so as to include only those processes which 

 are comparable to ordinary or external secretion. We must 

 only allow of the hypothesis of internal secretion in cells which 

 are of a glandular type, and we must diligently search for all 

 signs of cellular activity indicative of secretion. We must 

 further strive to study the process of secretion itself, to discover 

 the products of secretion, to trace them out into the blood- 

 stream, to follow them to their place of activity, and to find 

 their ultimate destination. 



In the next chapter we shall study some of the methods of 

 such investigations. 



