METHODS 



143 



The living being, having three different scales of activity, 

 is a wonderful transformer of energy. In the example of 

 the waterfall charging the accumulator, the dynamo is an 

 intermediary between the mechanical energy of falling 

 water and the chemical energy of the oxidized lead plates. 

 In the same way, in the living being the colloid mechanism 

 is an intermediary between chemical phenomena and 

 mechanical phenomena. 



When we compare, from this point of view of the Conser- 

 vation of Energy, two successive states of a living machine, 

 we have to take into account, not only what it receives from 

 its environment, but also the provisions of mechanical, 

 colloid and chemical energy accumulated in the individual 

 at the two times chosen for the comparison. This is very 

 complicated. When a blacksmith has worked his forge 

 for two hours, it is not easy to measure the quantity of 

 mechanical work he has furnished, the quantity of oxygen, 

 of reserves and foods he has consumed, the quantity of muscle 

 he has constructed by functional assimilation, the quantity 

 of sweat, water- vapour, carbonic acid, etc., which he has 

 lost. And yet all this would be necessary to strike the 

 balance of his profits and losses. 



The most difficult of all to measure I would even say 

 impossible is the consumption of the reserves localized in 

 the tissues and the fabrication of living substance, such as 

 that of the muscles. By the scales we can only know the 

 total weight of the individual ; but whether inside of him 

 there has been a substitution of living substance for reserve 

 substances we cannot ascertain. So we have to make ex- 

 periments of very long duration to find out the food value of 

 given substances a practical side of studies of energy in 

 biology. 



Interesting as this problem is, we cannot dwell on it here. 



