RESEARCH SEMINAR. 237 



of fish in ponds or aquaria. The only remedy in the case of the 

 adults is to remove them carefully from the fish, but further 

 trouble can be avoided by a plentiful introduction of small sur- 

 face fish, sticklebacks, minnows, etc., which will eat up the 

 larvae of the parasitic copepods. 



July 26. The Nature of the Heart-Rhythm. By A. J. CARLSON. 

 The following points were demonstrated on the heart of Liundns. 



1. The heart-beat is neurogenic, not myogenic. The heart- 

 muscle is not automatic under the normal conditions of life. 

 Extirpation of the ganglion or nerve-cord on the dorsal side of 

 the heart abolishes the rhythm at once and permanently, the 

 muscle contracting only on artificial stimulation. 



2. Coordination or conduction in the heart takes place in the 

 nervous and not in the muscular tissue. The entire heart, save 

 the median nerve-cord and the lateral nerves, may be cut trans- 

 versely. This does not affect conduction or coordination. Sever- 

 ing the nerve-cord and the lateral nerves, leaving the heart- 

 muscle intact, abolishes coordination of the ends of the heart at 

 either side of the lesion, the contraction not passing the level of 

 the lesion in either direction. 



3. The inhibitory nerve-fibers act on the ganglion cells in the 

 heart and not on the heart-muscle. Cardiac inhibition falls 

 within the category of inhibition of automatic or reflex neural 

 processes. 



August 2. Toxic and Antitoxic Action of Salts. By ALBERT 

 P. MATTHEWS. 



August 6. Causes of Blue and Green in Feathers. By R. M. 



STRONG. 



There are no blue pigments known in feathers, excepting one 

 possible case cited by Hacker, and green feathers rarely owe their 

 colors to green pigments. The blues are so-called structural 

 colors confined to the barbs, usually. 



Walter's hypothesis that these phenomena are surface colors 

 produced by underlying melanin pigments is untenable because 

 the pigments when isolated are not blue but dark brown. 



There are serious objections to the turbid medium hypothesis 

 of Hacker and others. Experimental studies indicate that most 



