WORK AND WASTE 



bonate of lime, because the quantity of carbonic acid ^ in 

 ordinary air is so small as to be inappreciable in this way. 

 But if the air which passes out is made to take the same 

 course, the lime-water will soon become milky, from the 

 precipitation of carbonate of lime, showing the presence 

 of carbonic acid, which, like tlie heat, is given ofi' by the 

 man. 



Again, even if tlie air be quite dry as it enters the cham- 

 ber (and the chamber be lined with some material so as to 

 shut out all vapour from the melting ice walls), that which 

 is breathed out of the man, and that which is given off 

 from his skin, will exhibit clouds of vapour ; which vapour, 

 therefore, is derived from the body. 



After the expiration of the hour during which the ex- 

 periment has lasted, let the man be released and weighed 

 once more. fTe will be found to have lost weight. 



Thus a living, active man, constantly does mechanical 

 ■work, gives off heat, evolves carbonic acid and 

 ■water, and undergoes a loss of substance. 



Plainly, this state of things could not continue for an 

 unlimited period, or the man would dwindle to nothing. 

 But long before the effects of this gradual diminution of 

 substance become apparent to a bystander, they are felt 

 by the subject of the experiment in the form of the two 

 imperious sensations called hunger and thirst. To still 

 these cravings, to restore the weight of the body to its 

 former amount, to enable it to continue giving out heat, 

 water, and carbonic acid, at the same rate, for an indefinite 

 period, it is absolutely necessary that the body should be 

 supplied with each of three things, and with three only. 

 These are, firstly, fresh air ; secondly, drink — consisting 

 of water in some shape or other, however much it may be 

 adulterated ; thirdly, food. That compound known to 



• By "carbonic acid" we mean "carbonic acid gas." This should in 

 strictness be called carbon dioxide (CO2), carbonic acid being the com- 

 pound of this with water, H2CO3. But for simplicity's sake, and 

 because the expression " carbonic acid " is in general use and is 

 generally understood to stand for carbon dioxide, we shall use it 

 throughout this book. 



