82 CONTRACTILE ELEMENTS. 



it only by the intermediation of terminations of the motor 

 nerves which it contains. Of the numerous facts which 

 refute this theory, and demonstrate the direct irritability of 

 the muscle, we will mention only the two following : 



There are certain poisons (woorara) which render the 

 motor nerves completely incapable of action, and, conse- 

 quently, powerless to convey any irritation to the muscles ; 

 and yet, in this case, the muscles which are directly excited 

 can pass from the first to the second form (Cl. Bernard, 

 Kolliker) ; the ultimate and fine ramifications of nerves 

 which they contain are not affected by this irritability, for 

 the poisons in question deprive of vitality especially the intra- 

 muscular terminations of the nerves (Vulpian). 



A motor nerve separated from the cerebro-spinal axis loses 

 all excitability after four days : the muscle, on the contrary, 

 previously innervated by this nerve, is still directly excitable 

 more than three months after (if only its connection has 

 been kept up with the sensitive nerves, and the raso-motors, 

 which provide for its nutrition. Longet). 



Variations of Irritability. This irritability belongs, 

 thus, really to the muscle itself, but it is modified by dif- 

 ferent circumstances, all of which may be said to modify the 

 nutrition of the muscle, or its chemical composition. This 

 is the effect of too prolonged repose. Moderate exercise, 

 which causes a greater interchange between the muscle and 

 the blood, keeps up the nutrition of the muscle, while a con- 

 trary effect is produced by fatigue or permanent contraction, 

 by means of which acids accumulate in the muscle, and the 

 alkalinity necessary to the preservation of its properties is 

 lost; thus, a short time after death the muscle ceases to be 

 irritable, the circulation no longer furnishing the materials 

 necessary to its support. The period at w r hich the irritability 

 disappears varies in different animals, being apparently shorter 

 in those whose nutrition is most active ; that is, in those whose 

 muscle consumes most quickly the materials left by the cir- 

 culation : the time being considerably longer in the case of 

 the cold-blooded animals. It varies, however, in an animal, 

 in different muscles, and even in different parts of the same 

 muscular organ : thus the left ventricle of the heart is one of 

 the first muscles to die, while the right auricle keeps its irri- 

 tability longer than any other muscle of the body, and has 

 thereby gained the name of ultimum moriens. 



Cadaveric Rigidity. The muscle, having lost its irrita- 

 bility, passes into the state which we have already spoken of 



