126 LIFE AND DEATH. 



measurement of the vital energy itself, for the origin 

 of which we must go back to the food. If the flux is 

 divided into two currents, mechanical and thermal, 

 they must both be measured and the sum of their 

 values taken. If the animal does not produce me- 

 chanical work, and all ends in heat, we have only to 

 capture, by means of a calorimeter, this energetic flux 

 as it emerges, and thus measure in magnitude and 

 numerically the energy in motion in the living being. 

 Physiologists use for this purpose various types of 

 apparatus. Lavoisier and Laplace used an ice calori- 

 meter — that is to say, a block of ice in which they 

 shut up a small animal, such as a guinea-pig; they 

 then measured its thermal production by the quantity 

 of ice it caused to melt. In one of their experiments, 

 for instance, they found that a guinea-pig had melted 

 341 grammes of ice in the space of ten hours, and had 

 therefore set free 27 Calories. 



But since those days more perfect instruments have 

 been invented. M. d'Arsonval employed an air calori- 

 meter, which is nothing but a differential thermometer 

 very ingeniously arranged, and giving an automatic 

 record. Messrs. Rosenthal, Richet, Hirn and Kauf- 

 mann, and Lefevre have used more or less simplified 

 or complicated air calorimeters. Others, following 

 the example of Dulong and Despretz, have used 

 calorimeters of air and mercury, or with Liebermester, 

 Winternitz, and J. Lefevre (of Havre), have had 

 recourse to baths. Here, then, there is a considerable 

 movement of research which has led to the discovery 

 of very interesting facts. 



Measurement of the Supply of Alimentary Energy 

 by the Chemical Method. — We may again reach our 

 result in another way. Instead of surprising the cur- 



