378 THE POPULAR SCIENCE MONTHLY. 



form in which it can be appreciated by those non-specialists most in- 

 terested in the subject involved. 



It is thus, to a certain extent, with the subject of the source of 

 muscular power in the animal organism. It is needless to specify in 

 this particular. Text-books and popular articles touching on the sub- 

 ject are continually asserting, as apparently unquestioned, theories 

 which at the present time are either exploded or very much in doubt. 

 It would seem, therefore, not without value to attempt, as far as prac- 

 ticable in a popular or semi-popular article, a general statement of the 

 present condition of the theories on the source of muscular power, 

 and of the main points of the evidence which tends to support these 

 theories. 



The genei'al acceptance of the law of the conservation and corre- 

 lation of physical forces had at once an important influence in direct- 

 ing attention to the source of muscular force. The idea was readily 

 taken up that this form of force is at the expense of heat, which is 

 produced by the oxidation of carbon and hydrogen in the body, the 

 necessary oxygen being conveyed by the arterial blood to the mus- 

 cular tissue. In other words, the somewhat trite comparison of the 

 human body and the muscular system to an engine, which consumes 

 just so much fuel to produce so much force, has pretty clearly formu- 

 lated the idea as generally accepted. And so far as it goes the com- 

 parison is not bad. 



When, however, we pass beyond this somewhat vague simile to 

 an examination of the more intimate nature of these various processes, 

 we find the questions raised are not so generally understood. Accept- 

 ing that the muscular force is produced by the ultimate oxidation of 

 carbon and hydrogen to carbonic-acid gas and water respectively, the 

 next questions that suggest themselves are : " What is the immediate 

 source of this carbon and hydrogen — the fuel material for muscular 

 force ? " and " What is the real nature of these processes which we 

 call briefly oxidation?" The endeavors to answer these questions 

 have given rise to many discussions and disputes, which are, even at 

 the present day, by no means concluded. 



Before taking up the discussion of the theories advanced to answer 

 these questions, it will not be out of place to review very briefly the 

 composition of the muscles and their general relations to the circula- 

 tion — only in so far, however, as is necessary for a clear comprehension 

 of the evidence and arguments involved in the discussion. 



A muscle is essentially a collection of lengthened cells held together 

 by a connective tissue. Each cell consists of a delicate cell- wall or 

 membrane containing a fluid or semi-fluid mass of living (protoplasmic) 

 matter. This gelatinous substance possesses the power of contrac- 

 tion under the stimulus of excitations of various kinds — nervous im- 

 pulse, electricity, heat — and the cell becomes thereby shortened. This 

 process, taking place simultaneously in all the cells of a given muscle 



