NEUROHUMORS 49 



group of cells, for their processes are so richly branched 

 and intertwined that the necessary contacts for such a 

 transmission must be more than abundant. 



The conception to which we are finally led respecting 

 the control of melanophores in Fundulus is as follows: 

 this control is accomplished through two sets of auto- 

 nomic nerves, concentrating and dispersing, and, though 

 it is what would be termed a strictly nervous control, 

 it is nevertheless based upon a special type of hormone, 

 a neurohumor, which ordinarily passes directly from the 

 nerve terminal to the effector cell, the melanophore, 

 over an almost submicroscopic distance, but under other 

 circumstances may make its way over stretches of a 

 millimeter or two from its region of origin to distant 

 effectors by way of the lipoid constituents of the inter- 

 vening tissues. 



As a fish from which to attempt the extraction of an 

 oil-soluble neurohumor, Mustelus is much more favor- 

 able than Fundulus. The phase of Mustelus that is 

 suspected of being associated with such a neurohumor 

 is the pale one, and the parts that show this phase to 

 best advantage are the fins. Dogfishes were therefore 

 put in a white-walled illuminated tank and after a few 

 days, when they had become fully blanched, they were 

 killed and their fins removed. It was a matter of good 

 fortune that in the preparation of the fins the cutting 

 of nerves intensified their paleness rather than the re- 

 verse. The fins immediately after their removal were 

 ground to a pulp in an ordinary kitchen grinder, and 

 the pulp from the fins of one ordinary dogfish was then 

 thoroughly mixed with about two cubic centimeters of 

 Italian olive oil. This mixture was further ground by 

 hand for about half an hour in a rough porcelain mortar 

 till it reached the consistency of a thick paste and then 

 it was set aside to undergo extraction. In most in- 



