238 THE ADRENAL SYSTEM AND VASOMOTOR FUNCTIONS. 



contractility is generally thought to be associated with nerve- 

 impulse, destruction of all nervous connection with a muscle 

 does not cause it to lose its excitability. Its inherent property 

 in this particular is shown by the fact that, although the apex 

 of the heart contains no nerve or nerve-cells, it nevertheless 

 responds to stimulation. Even when detached from the body, 

 muscles preserve their contractility for a time under suitable 

 conditions. This would appear to eliminate the need of fur- 

 ther energy to account for the phenomena witnessed; but the 

 contrary is the case, since it shows why muscular tissue, owing 

 to its inherent irritability, responds to various stimuli: vital, 

 electrical, physico-chemical, and mechanical. Electricity, we 

 know, acts as a powerful stimulus, but heat alone acts in pre- 

 cisely the same manner if the temperature is adequate and is 

 raised rapidly; marked contraction may thus be caused when 

 30 C. is reached, and violent activity induced before the mus- 

 cle is heated to 45 degrees. Chemical stimuli will produce the 

 same effect, provided the reaction induced occurs with suffi- 

 cient rapidity. 



That the nervous impulse is not the source of mechanical 

 energy utilized under these circumstances, is shown by the fact 

 that a chemical stimulus applied to a nerve, ammonia, for in- 

 stance, will not stimulate it though it will excite the muscle; 

 various acids, hydrochloric, acetic, etc., will give rise to the 

 same phenomena. "Certain poisons (curare) cause the motor 

 nerves to become completely incapable of action," says M. 

 Duval, "and, therefore, incapable of transmitting irritation to 

 a muscle; nevertheless, under these circumstances, the excited 

 muscle can directly pass from the state of rest to that of 

 activity (Claude Bernard, Kolliker); the ultimate and fine 

 nervous ramifications that they contain take no part in this 

 irritability, since the poisons referred to kill mainly the intra- 

 muscular endings of the nerves (Vulpian). A motor nerve 

 separated from the cerebro-spinal axis loses, after four days, 

 all excitability; the muscle, on the contrary, previously in- 

 nervated by this nerve remains directly excitable more than 

 three months (Longet)." 



That muscle is directly and independently excitable by a 

 large number of stimuli is evident; that oxygen should, 



