BIOELECTRIC PHENOMENA 335 



subject to variation in frequency. Such variations offer 

 some of the most beautiful examples of physiological 

 adjustment to the varying needs of the organism; e.g., the 

 respiratory rhythm of warm-blooded vertebrates. 



The normal rhythm of electromotor discharge may 

 be simple, i.e., there may be a regular succession of 

 single impulses, as in the sinus region which controls the 

 vertebrate heart beat; in this case both the unsummated 

 character of the muscular contraction and the form of 

 the galvanometric record show that in the sinus, auricle, 

 or ventricle a single electromotor variation corresponds 

 to each beat. In other cases, however, a rhythmical 

 succession of discharges may occur, each discharge 

 being itself rhythmical; this is the case, for example, 

 in the nerve cells innervating the respiratory muscles of 

 vertebrates. Garrey has recently observed a similar 

 condition in the Limulus heart ;^ corresponding to each 

 beat there is an oscillatory electrical variation or dis- 

 charge, undoubtedly originating in the ganglion, each 

 discharge exhibiting a constant number, about twelve, 

 of separate electromotor variations. The series or 

 "volley" of secondary waves or pulses forming each 

 discharge has its own rhythm, which is independent of 

 the cardiac rhythm as a whole. Change of temperature 

 changes the rate of oscillation in each. ganglionic "beat," 

 but the number of distinguishable oscillations always 

 remains about twelve. It appears to be a general rule 

 that the electromotor rhythms are influenced by temper- 

 ature in the same manner as most other physiological 

 rhythms, i.e., show the chemical temperature coefficient; 



^W. E. Garrey, unpublished observations at Marine Biological 

 Laboratory, Woods Hole, Massachusetts. 



