68 EXPERIMENTAL RESEARCHES 



possess sufficient nutrient matter to saturate 

 every avidity. The origin of the higher avidity 

 of the tumour cells is quite unknown to us ; for 

 this question means neither more nor less than 

 the last problem of tumour aetiology. 



An entirely different significance must be 

 ascribed to the specific growth-stimulating 

 bodies or " hormones," for the existence of 

 which we have received irrefutable proof chiefly 

 by the work of Starling. As you may know, he 

 observed lactation in non-pregnant females as 

 the result of injecting emulsions of embryos. 

 But, of course, I should never think of asserting, 

 as one might be led to think by von Dungern's 

 explanation of my views, that as the result of 

 over-nutrition a typical lactation might be set 

 up in a virgin. 



Such specific growth- stimulating bodies play 

 an important role also in other cases, and are 

 intimately connected with atreptic immunity. 

 Thus we know that the influenza bacillus cannot 

 do without haemoglobin for its growth. There- 

 fore it is quite easy to cultivate the bacillus 

 directly from the sputum, which almost always 

 contains small quantities of haemoglobin. But 

 if we do not artificially add haemoglobin to the 

 sub-cultures, the bacteria very soon die in them. 



