MUSCULAR CONTRACTION 



17 



small trace of calcium suffices to prevent these spontaneous 

 movements and bring about stoppage in the relaxed condition. 

 Similarly, removal of calcium brings about systolic stoppage 

 of the crustacean heart (Hogben). Mines also showed that 

 addition of Ca diminishes excitability of muscle towards 

 electrical currents of long duration. On the other hand, the 

 effect of increased calcium is to diminish relaxation in the plain 

 muscle of the crop of the fowl (Fienga) and the pharynx of 

 Aplysia (Hogben), while complete absence of calcium produces 

 diastolic arrest of the heart in Pecten (Mines), Raia, Scyllium 



Fig. 5. — Effect of excess of calcium on the perfused heart of the 

 lobster, Homarus (Hogben). 



and Rana (Mines) ; on the other hand, Lovatt Evans describes 

 diastolic arrest in the heart of Helix by excess of calcium. 



So far we have little information with respect to the specific 

 role of anions, though certain of these have very characteristic 

 effects, as illustrated in the universal action of cyanides in 

 depressing oxidative processes. The fact that proteins appear 

 to behave as amphoteric electrolytes and are found in the cell 

 in general on the alkaline side of their isoelectric point, thus 

 existing as metallic proteinates, is a valid reason for attach- 

 ing special significance to the relation of kations to biological 



