CHAP. IX.] THE CONTRACTILE TISSUES. .371 



of platinum wires melted through the sides of the tube, the wires 

 being adapted to an electrical apparatus for stimulation. The 

 absorption-tube was filled with salt solution after the muscle had been 

 fixed within it; and then inverted over a vessel containing a lower 

 stratum of mercury and an upper one of salt solution, in such a manner 

 that the open mouth of the tube passed through the upper layer 

 to the mercury. A bent tube proceeding from a reservoir of electro- 

 lytic hydrogen, or pure nitrogen, or air, or detonating gas, served to- 

 introduce the gas into the absorption-tube, and* at the same time 

 to drive out the salt solution. Muscles of different degrees of 

 thickness were kept under observation ; but the sartorius of the frog 

 was found to be peculiarly favourable for these experiments. The 

 results were not modified by previously curarizing the muscles. 



Tested in this manner, it appeared that the thickness of the 

 muscles had a singular influence on the result. The sartorius, of 

 large surface and small bulk, lived longer in hydrogen than in gases 

 containing oxygen; while thicker muscles agreed with the muscles 

 observed by Humboldt, in retaining their irritability longer in 

 oxygen. Another form of this experiment led to the same con- 

 clusions. If muscles were enclosed in tubes which were then made 

 as vacuous as possible, until nothing remained in them but traces of 

 carbon dioxide, the sartorius was found to live longer in the vacuum, 

 in the absence of oxygen, than in air ; while thicker muscles lost their 

 irritability sooner in the vacuum. It should be noticed that all 

 muscles exhibit an exalted irritability when first the vacuum is 

 produced. 



This influence of oxygen upon the irritability of thick and thin 

 muscles seems to admit of but one explanation. There are two 

 concurrent processes in muscles exposed to the air, in which oxygen 

 plays a part : one tends to destroy, the other to preserve irritability. 

 The former is, beyond doubt, the putrefactive process already demon- 

 strated in living and rigid muscle, which spreads the more rapidly 

 the greater the surface exposed. Hence in the thin sartorius the 

 process invades all parts of the tissue within a short time, and death 

 results : to defend the muscle from oxygen is to preserve it alive. On 

 the other hand, the second process implicating oxygen is a true 

 physiological process of revival. In the thicker kinds of muscles, whose 

 internal mass is long shielded from the putrefactive action of oxygen, 

 this process of revival is a marked benefit ; and hence the muscle 

 removed from the influence of oxygen by enclosure in a vacuum 

 more rapidly becomes enfeebled than one exposed to the air. 



Of the nature of this functional absorption of oxygen and process 

 of revival we have as yet no exact conception. The process itself 

 is but of small value in prolonging the normal irritability of frog- 

 muscles exposed to the air and of no appreciable moment in the 

 function of contraction ; but, as will be hereafter explained, it is- 

 extremely potent in restoring irritability to mammalian muscles 

 exhausted by interruption of their blood current (p. 380). It is 



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