34 THE STORY OF LIFE'S MECHANISM. 



space with arrangements for furnishing him with 

 air and food in measured quantity, and with 

 appliances for measuring accurately the work 

 he does and the heat given off from his body. 

 In addition, it is necessary to measure the exact 

 amount of material he eliminates in the form of 

 carbonic acid and other excretions. Such ex- 

 periments present many difficulties which have 

 not yet been thoroughly overcome, but they 

 have been attempted by several investigators. 

 For the purpose of such an experiment scientists 

 have allowed themselves to be shut up in a small 

 chamber six or eight feet in length, in which 

 their only communication with the outer world 

 is by telephone and through a small opening in 

 the side of the chamber, occasionally opened for 

 a second or two to supply the prisoner with 

 food. In such a chamber they have remained 

 as long as twelve days. In these experiments 

 it is necessary to take account not only of the 

 food eaten, but of the actual amount of this food 

 which is used by the body. If the person gains 

 in weight, this must mean that he is storing up 

 in his body material for future use ; while if he 

 loses in weight, this means that he is consuming 

 his own tissues for fuel. Careful daily records 

 of his weight must therefore be taken. Esti- 

 mates of the solids, liquids, and gases given off 

 from his body must be obtained, for to carry 

 out the experiment an exact balance must be 

 made between the income and the outgo. The 

 apparatus devised for such experiments has been 

 made very delicate ; so delicate, indeed, that the 

 rising of the individual in the box from his chair 



