414 Prof. Th. W. Engelmarm. [Mcar. 14, 



This quantitative composition and this minute consumption of the 

 active muscle compel us to assume that relatively only very few 

 molecules of the muscular substance can be considered as sources of 

 energy, and of these again it is generally but a small part that at 

 a certain moment perform their function. How else were it possible 

 for a severed bloodless muscle to continue to carry out, without any 

 perceptible decrease of weight, many thousands of contractions, and 

 how else could a frog's heart, isolated and all but bloodless, beat on 

 for days together, with a nearly constant frequency and v ut slowly 

 sinking power ? 



With certain presuppositions we may compute the quantity of 

 matter through the chemical action of which the amount of actual 

 energy, produced at a certain contraction, must have been generated. 



If we prevent a muscle from doing external work during the 

 contraction, the whole actual energy will present itself in the shape 

 of heat. When there is but a slight contraction, the muscle of a frog, 

 e.g., will grow warmer by about O'OOl C. Supposing the specific 

 heat of the muscle to be equal to that of water (in fact it is less), 

 we find that to produce a rise of 0*001 C. in temperature a quantity 

 of heat of O'OOl cal. is required for each gram of muscle. No matter 

 whether this quantity of heat results from combustion of carbo- 

 hydrates, fats, or albuminous matter, it can be but an infinit- 

 esimal part of the muscular substance that produced it. If, e.g., 

 as is ordinarily supposed, the combustion of a carbohydrate into 

 C0 2 and H 2 produced that heat, taking the heat of combustion of 

 one gram of carbohydrate to be broadly 4000 cal., no more than a 

 four thousandth part of a milligram will have been consumed in each 

 gram of the muscle. Hence only about a four millionth part of the 

 muscular substance could have been the source of the actual energy, 

 set free by the stimulus, and have served at the same time, according 

 to the above hypothesis, as the seat of direct attraction. 



But whatever may be our conception of the size, form, position, 

 and sphere of action of this four millionth part with regard to the rest 

 of the soft, watery mass, only passively moved, I fail to understand 

 how, through direct chemical attraction, this one particle should set all 

 those other four million parts, less one, moved, as in fact it does. 



We must not forget that we have to deal with enormous changes 

 of form. Muscles of insects are sometimes shortened by local 

 contraction to one twentieth of their length during rest. The 

 myopodia of Acanthocystis can be reduced to a fiftieth part of their 

 length by the action of even a weak stimulus ; in this case an 

 extremely long, thin fibre is in a moment changed into a short 

 cylinder, about as broad as it is long. 



That this can ever be brought about by direct chemical attraction, 

 seeing that but a relatively infinitesimal part of the soft watery sub- 



