in its Relations to Physiology. 421 



Thus it has been ascertained that the average duration of human 

 life is thirty and some years, and yet it is precisely at the age of thirty 

 that the smallest proportion of individuals die. All these figures come 

 as near to truth as it is possible to arrive ; they are, therefore, consi- 

 dered as really and exactly correct, and serve as the basis of calculation 

 for the terms of tontines and life-assurances, or for fixing the weight 

 of the arms and baggage a soldier may bear. 



The strictly scientific physiologist is not satisfied with this ; observa- 

 tions taken from nature on this scale do not convince him. Regardless 

 whether an individual or an animal has partaken previously of a repast 

 or not, without troubling himself whether with a full or an empty sto- 

 mach, he shuts him up in a cage and determines the amount of oxygen 

 which he inhales, and the quantity of carbonic acid which he exhales. 

 Instead of weighing the tobacco and its asheg, he weighs the smoke ! 

 as if the sources of error were not a thousand times more obvious and 

 considerable in this method than in the former ! But supposing even 

 this determination were exactly correct, what information does it afford 

 him ? Neither more nor less than the amount of what an individual, 

 shut up in such a cage, inhales and exhales under certain circumstances, 

 not very minutely examined, and which do not, at any rate, correspond 

 with the normal state. But it does not inform him how much carbon 

 this individual consumes in twenty-fours hours. If the experimentalist 

 had given a bottle of good wine to the individual in the cage, or if the 

 latter had taken a copious draught of cod-liver oil previously to enter- 

 ing into the cage, very different proportions would undoubtedly have 

 resulted. 



One of my friends has, for 212 days, taken two ounces of cod-liver oil 

 per diem, or a sum total of thirty-five pounds and a quarter, during that 

 period, without increasing in weight; his faeces, upon examination, 

 have been found to contain no trace of the oil. Now, if from this we 

 infer that these thirty-five pounds and a quarter have been eliminated 

 by the skin and the lungs, having served for the support of the respir- 

 atory process, what can be rationally objected to such a conclusion? 

 This individual, from the moment he began to take liver-oil, could no 

 longer drink wine, precisely because both these substances mutually 

 prevent their elimination in the normal way, that is, in the form of oxygen 

 compounds. But still the physiologist is unsatisfied, and repeats his 

 " Prove it !" When I show him that the amount of carbon which a 

 full-grown individual, in a state of free motion and labour, consumes, 

 accounts sufficiently for the evolution of heat in his organism, he 

 replies, " This proves nothing, for we do not even know what heat is ; 



