GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 137 



below 0° 0. it again becomes less, until at the freezing-point of muscle no con- 

 traction is obtained. The cause of these peculiar phenomena is not definitely 

 understood. 



(/) Effect of Drugs and Chemicals upon Muscular Contraction. — Certain drugs 

 and chemicals have a marked effect upon the irritability (see p. 58) and con- 

 ductivity (see p. 93) of muscles, and these effects must necessarily find expres- 

 sion in the amount of contraction which would be excited by a given irri- 

 tant. In addition to this, it is worthy of notice that the character of the con- 

 traction may be altered. 



The drug which has the most striking effect upon the form of contraction is 

 veratria. A few drops of a 1 per cent, solution of the acetate of veratria, 

 injected into the dorsal lymph sac of a frog whose brain has first been 

 destroyed, in a few minutes alter completely the character of the reflex 

 movements : the muscles are still capable of rapidly contracting, but the con- 

 tractions are cramp-like, the power to relax being greatly lessened. The 

 poison acts upon the muscle-substance, and even a very small dose applied 



Fig. 61.— Myogram of muscle poisoned with veratria and that of a normal muscle : a, myogram from a 

 normal gastrocnemius muscle of a frog— the waves at the close are due to the recoil of the recording lever; 

 b, myogram from a gastrocnemius muscle poisoned with veratria. recorded at the same part of the drum. 



directly to the muscle for a few hours — e. g., a solution containing 1 part to 

 100,000 of 0.6 per cent, solution of sodium chloride — suffices to greatly alter 

 the character of the contraction called out by various irritants. 1 If a muscle 

 poisoned with veratria be isolated and connected with a myograph, a contrac- 

 tion excited by a single induction shock will show a rise as rapid, as high, 

 and as strong as normal, but the fall of the curve will be greatly prolonged 

 (see Fig. 61). Often the crest of the curve will exhibit a notch, which shows 

 that relaxation may begin and be checked by a second contraction process 

 which carries the curve up again and holds it there for a considerable time. 

 In the above experiment the contracture effect followed the primary contrac- 

 tion immediately. The nature of the contracture of a muscle poisoned with 

 veratria has been considered (sec p. 130). 



There arc a number of drugs which have an action on muscle-tissue simi- 

 lar to that of veratria — e.g., cornutinc 2 produces a similar effect on striated 

 muscles; digitaline increases the tonus of hearl muscle and of the smooth 



'Bucannan: Journal of Physiology, 1899, xxv. p. 137. 

 * Cushny : Pharmacology and Therapeutics, 1899. 



