726 HANDBOOK OF PHYSIOLOGY. 



substances so formed artificially is constantly increasing; and there 

 seems to be no reason for doubting that even such as albumen, gelatin, 

 and the like will be ultimately produced without the intermediation of 

 living structure. 



The formation of the latter, such an organized structure for instance 

 as a cell or a muscular fibre, is a different thing altogether. There is at 

 present no reason for believing that such will ever be formed by artificial 

 means; and, therefore, among the peculiarities of living force-transform- 

 ing agents, must be reckoned as a great and essential .one, a special inti- 

 mate structure, apart from mere ultimate or proximate chemical com- 

 position, to which there is no close likeness in any artificial apparatus, 

 even the most complicated. This is the real distinction, as regards com- 

 position, between a living tissue and an inorganic machine; namely, the 

 difference between the structural arrangement by which force is trans- 

 formed and manifested anew. The fact that one agent for transforming 

 force is made of albumen or th3 like, and another of zinc or iron, is a 

 great distinction, but not so essential or fundamental an one as the differ- 

 ence in mechanical structure and arrangement. 



In proceeding to consider the difference between what may be called 

 the transformation-products of living tissue, and of an artificial machine, 

 it will be well to take one of the simple cases first the production of 

 mechanical motion; and especially because it is so common in both. 



In one we can trace the transformation. We know, as a fact, that 

 heat produces expansion (steam), and by constructing an apparatus 

 which provides for the application of the expansive power in opposite 

 directions alternately, or by alternating contraction with expansion, we 

 are able to produce motion so as to subserve an infinite variety of pur- 

 poses. For the continuance of the motion there must be a constant sup- 

 ply of heat, and therefore of fuel. 



In the production of mechanical motion by the alternate contractions 

 of muscular fibres we cannot trace the transformation of force at all. 

 We know that the constant supply of force is as necessary in this 

 instance as in the other; and that the food which an animal absorbs is 

 as necessary as the fuel in the former case, and is analogous with it in 

 function. In what exact relation, however, the latent force in the food 

 stands to the movement in the fibre, we are at present quite ignorant. 

 That in some way or other, however, the transformation occurs, we may 

 feel quite certain. 



There is another distinction between the two exhibitions of force 

 which must be noticed. It has been universally believed, almost up 

 to the present time, that in the production of living force the result is 

 obtained by an exactly corresponding waste of the tissue which produces 

 it; that, for instance, the power of each contraction of a muscle is the 

 exact equivalent of the force produced by the more or less complete 



