428 E. V. COWDEY 



tions, which seems to pass first into the intercellular spaces, and thence 

 into the capillaries, as is indicated in Fig. 3. Thus far the substance in 

 question has not been seen in fresh preparations, nor has it been specifically 

 stained with any vital dye. Obviously, the correct method of approach 

 is to trace this material throughout the life cycle of the interstitial cells 

 of some common laboratory animal and ascertain, if possible, whether it 

 varies either quantitatively or qualitatively with alterations in the physio- 

 logical activity of the cells. Experimental procedures should also be re- 

 sorted to. It is claimed, for instance, that removal of one testicle pro- 

 duces a compensatory hypertrophy in the interstitial cells of the other 

 which may have some influence on the secretion. The chances of obtain- 

 ing decisive results are good, because, in the past, investigators have paid 

 more attention to the conditions which alter the number of the interstitial 

 cells and have rather avoided the minute but significant alterations which 

 occur in their structure and chemical reactions. 



