230 THE POPULAR SCIENCE MONTHLY. 



sugar, or fat, or proteids, it has already undergone complete combus- 

 tion. It can not, like them, unite any further with oxygen and thus 

 supply energy. 



And yet it is more essential to life than any of them, for without 

 it the products of waste can not be removed from the tissues, and the 

 vital fires, so to speak, are smothered in their own ash. If we take the 

 excised muscle of a frog and stimulate it to repeated contraction, the 

 contractions become feebler and feebler, until at last they cease alto- 

 gether. But this is not because the fuel which the muscle contains in 

 itself has been so completely burned up that none of it is left to fur- 

 nish the requisite energy to the muscle ; it is because the chemical pro- 

 cesses necessaiy to the contraction of the muscle are arrested by the 

 accumulation of the products of its own waste. If we wash these out 

 of the muscle by sending through its vessels a weak solution of -com- 

 mon salt, which supplies to it no new material, but which removes 

 these waste products, the contractile power of the muscle will be re- 

 stored. 



This restoration takes place still more quickly and thoroughl}^ if 

 we employ a fluid which will sixpply oxygen, such as a solution of per- 

 manganate of potash, instead of a simple solution of salt, which merely 

 washes out the muscular waste. The muscle is like a fire in the grate, 

 which goes out long before the coal is entirely consumed, on account 

 of the ash which smothers it, and just as we can revive the smoldering 

 embers by supplying them with oxygen by the use of bellows, so the 

 muscle revives more quickly when its supply of oxygen is increased. 

 The quicker the fire burns the sooner will it be choked in ash, and the 

 more rapidly the muscle contracts the sooner will it lose its powers. 



The same is the case with the heart. The slowly beating heart of 

 a crocodile will pulsate for a day or more after it has been cut out of 

 the body, but the rapidly pulsating heart of a mammal will very soon 

 cease to beat ; and, the more rapidly it has been beating before the 

 animal's death, the sooner will it cease to contract afterward. If the 

 vagi are cut in the living animal so that the cardiac pulsations become 

 excessively rapid, the heart's movement ceases almost as soon as the 

 animal dies ; but, if during life the vagi are irritated so as to make the 

 heart contract very slowly indeed, it comes to resemble more nearly 

 the heart of the crocodile, and continues to pulsate for a considerable 

 time after the animal's death. The heart, too, resembles voluntary 

 muscles, inasmuch as, if we wash out of it the products of its own waste, 

 it will continue to beat for a much longer time than if we allow them to 

 accumulate. By simply allowing a saline solution to circialate through 

 the heart of a frog it may be kept beating for many hours longer than 

 if it were left to itself. Both voluntary muscles and involuntary ones, 

 such as the heart, cease to act, almost invariably, not by exhaustion 

 of their energy -yielding substance, but by accumulation of the waste 

 products within them ; and muscles, both voluntary and involuntary, 



