THE MECHANISM OF LIFE 553 



c. The Source of the Energy of Muscle 



Although thus far but few investigations have been made by 

 physiologists upon the mechanics of the transformation of energy 

 in living substance in general, this is not true of one particular 

 class of these phenomena. This class comprises the movements of 

 contraction and expansion. The mechanics of muscle-contraction 

 especially, in which energy is developed with most remarkable and 

 most astonishing power, has from early times engaged very actively 

 the attention of physiologists, and the number of theories that 

 have been formed regarding the mechanics of muscular movement 

 is only a little smaller than the number of investigators who have 

 studied the problem thoroughly. An interesting chapter in the 

 history of human thought is reflected in these theories from the 

 time of Galen down to the present day, and it is pleasing to 

 one's historic sense to trace these theories from their very naive 

 beginnings. Whoever is interested in this bit of physiological 

 history will find the literature of the older theories down to the 

 preceding century collected by Haller (1762). Hermann ('79) has 

 given the essentials of the later theories in his Handbuch der 

 Physiologic, and the newest views, so far as they possess interest, 

 are collected and critically examined in a work that has recently 

 appeared, 1 which considers the old problem from the comparative, 

 cell-physiological side. 



Without a doubt, of all the activities of organisms, muscle-work 

 is that in which the greatest transformation of energy takes place 

 in the shortest time. The quantity of energy that is set free in 

 muscle-activity, as is well known, is astonishing. Hence the 

 question presents itself : of the energy introduced into the body 

 what portion affords the energy that is thus set free, in other words, 

 where is the source of muscle energy to be sought ? 



It is evident that the source must be chemical energy, for the 

 animal-body performs its labours by means of chemical energy ex- 

 clusively. But which of the food-stuffs introduced into the body 

 afford by their transformation the chemical energy necessary to 

 muscle activity ? Is it the proteids, or is it the carbohydrates and 

 the fats ? 



An active contest, which very recently has become augmented, 

 has been carried on over this question. The original and very 

 clear theory of Liebig ('57, 70) that proteid as the chief constituent 

 of muscle must be the source of its work, was attacked during its 

 author's lifetime, and it has since been thought for decades that in 

 place of Liebig's view the correct solution of the problem had been 

 found. The argument that led to this idea, which has prevailed 

 to the present time, is interesting. It was said : if the source of 

 1 Cf. Verworn ('92, 1). 



