54 GRAHAM LUSK 



blame. It was an error to assume that, if urea were an end-product of the 

 oxidative metabolism of muscle, then one could measure the intensity of the 

 work done by the quantity of urea in the urine. 



The first facts contradicting the idea that urea is a measure of muscular 

 activity were communicated by Bischoff and by Bischoff and Voit of Munich, 

 which researches are to be considered as the extension of work accomplished in 

 Giessen. It is hardly necessary to state that these experiments always excited 

 my keenest interest because they were effected with my method of urea determi- 

 nation. . . . 



These experiments firmly establish the fact that, although urea elimination 

 is a measure of protein ingestion and metabolism, it is not a measure of the 

 work done by the body. 



When one thinks these matters over it is apparent that the facts could 

 not be otherwise. For if the metabolism of the muscle increased with work a 

 man could exhaust his entire supply of muscle tissue, because work is directed 

 by the will. 



He criticizes Frankland's comparison of the muscle with a steam 

 engine, as follows: 



It is certain that the wonderful structure of the animal body and of its 

 parts will long and perhaps forever remain an insoluble riddle. But the proces- 

 ses within the organs are of chemical ancj physical nature, and it is incompre- 

 hensible that oxygen and combustible materials are under the control of nerves 

 to induce their union. The factor of voluntary nerves upon muscle activity 

 must be of a different order. . . . 



I consider that those investigators who have busied themselves with the 

 question of the source of muscular power have thought its solution too simple 

 and that it will be many years before a proper viewpoint leads to clarity in the 

 solution of this subject. I have no desire to enter into the dispute. 



Liebig discusses the activity of the yeast cell as follows: 



A close consideration of the behavior of the yeast cell may be desirable in 

 order to give a more definite idea of what transpires in living muscle. 



It is certain that motions occur within the yeast cell through which it is 

 enabled to accomplish external work. This work consists in the cleavage of 

 carbohydrates and similar substances. This is chemical work; it would "be 

 mechanical work if the yeast were able to split wood, which is likewise carbo- 

 hydrate. 



One part of yeast can destroy sixty parts of its weight in sugar, according: 

 to Pasteur. A gram of yeast can produce the heat equivalent of 148,960 gram 

 meters of work without the intervention of oxygen. 



The cause of all these activities lies in the motions of the contents of the 

 yeast cells. 



In similar manner the motions of life are present in muscle cells, without 

 muscular contraction resulting. When the movement within the muscle cells 

 rises. above a certain limit, muscular contraction follows. 



Liebig enters into a defense of the use of Liebig' s extract of meat. 

 At one time he had regarded it, when mixed with potatoes, as the equiva- 

 lent of meat. He quotes Hippocrates: 



