BIOLOGY. 287 



increase takes place in the excretion of urea after even violent 

 exercise. Whatever may prove to be the fate of the nitrogenous 

 elements of muscular tissue, there can be scarcely any doubt but 

 that there is a large extra consumption of hydro-carbonaceous 

 material during muscular action. It is just possible to conceive 

 that the increase of waste products which can be observed in a 

 muscle, after a series of contractions, may belong not to the time 

 of contraction itself, but to the stage immediately following, — may 

 indicate, as it were, a kind of reaction following the shoc-k of the 

 stimulus ; but there is nqt the shadow of a proof that such is really 

 the case. It may be taken for granted that muscular contraction 

 means increase of chemical action, and, therefore, increase in the 

 total amount of " actual energy" issuing from the muscle. 



_ With regard to one of the forms of energy proper to muscles, — 

 viz., electricity, — we have known for some time past, that during 

 contraction, a remarkable change occui-s in the " muscle-current." 

 It is generally spoken of as "the negative variation," and has 

 been made the basis of Voit's, as well as of Dr. C. B. RadcliflFe's, 

 views on the subject we ai"e dealing with. 



The production of heat during muscular contraction has re- 

 ceived much attention during the last few years. We need not 

 specify the various observations here ; and Heidenhain contends 

 that the delicacy of his own arrangements have enabled him to 

 detect and avoid the en-ors of his predecessors. Frogs' muscles 

 were used for the experiments. His results are briefly these : — 



1. During a contraction (that is, a single contraction, not a 

 tetanus), heat is always given out, the index of the apparatus 

 showing a rise of temperature varying from .001° C to .005° C. 



2. When a muscle (suspended by one end, and with a weight 

 attached to the other) is stimulated by a stimulus of constant 

 strength, and loaded with a variable Aveight, both the heat given 

 out and the work done (weight -\- heat) increase with an in- 

 crease of the weight up to a certain limit (determined by the 

 condition of the muscle), beyond which they both sink. 



3. When a muscle is stretched by a weight hung at one end, 

 but is prevented from contracting by being fixed at both ends, 

 the amount of heat given out (on the application of a stimulus of 

 the same strength) varies directly as the extending weight, up to 

 a certain limit. 



4. When a muscle, excited by the same stimulus and bearing 

 the same weight, is in one case allowed to contract freely, but iu 

 another prevented from so doing by being fixed at both ends, the 

 amount of heat given out on the stimulus being applied is much 

 greater in the latter instance than in the former. 



5. When a muscle is connected with a small constant weight 

 and a large variable one, in such a way that it always bears the 

 strain of the former, but that of the latter only at such times as it 

 contracts, both the heat given out and the work done (with the 

 stimulus of same strength) vary directly as the larger weight. 



6. When the experiment is repeated with the alteration that the 

 smaller weight, whose strain is continually borne, is made variable, 

 and the larger one constant, both heat and work vary directly as 

 the variable weight. 



