PHILOSOPHICAL SOCIETY OF WASHINGTON. 55 



these are questions which have taxed the utmost resources of in- 

 vestigators, and as to which our knowledge is yet in its infancy. 



On the other hand, the direct measurement of the resulting heat 

 and work has hitherto proved still less satisfactory. It would seem 

 to be a very simple thing to place an animal in a calorimeter, and 

 measure the heat-units evolved in a given time, as Lavoisier and 

 Laplace attempted to do in the latter part of the last century, and 

 we have been told that "Lavoisier's guinea-pig placed in the cal- 

 orimeter gave as accurate a return for the energy it had absorbed 

 in its food as any thermic engine would have done." 6 But this 

 assertion is not supported by the results of actual experiment. We 

 know now that many precautions, unknown to Lavoisier, must be 

 taken to secure any approach to accuracy in calorimetric experi- 

 ments with animals, and just as the method is being brought to 

 something like perfection by arranging for the respiratory process 

 and its influence on the results, and by other necessary modifications 

 of the primitive rude attempts, 7 doubts are beginning to arise 

 as to whether after all the conditions in which the animal is placed 

 in the calorimeter are not so far abnormal as seriously to vitiate the 

 results; 8 so that in fact the most approved numerical expressions of 

 the heat-production of the body to be found in the books are based 

 rather upon calculation of the amount that ought to be produced 

 by the oxidation of an estimated quantity of food than upon actual 

 calorimetric observations. 



Nor do we find it any easier when we attempt the actual meas- 

 urement of the amount of work produced by an animal from a 

 given amount of food. Indeed, in attempting to formulate an 

 equation between the potential energy of the food and the actual 

 amount of heat and work in any given case, we are met with the 

 special difficulty that the animal does not evolve less heat because 

 it is doing work than it does when it is at rest ; on the contrary, it 

 actually evolves more heat, consuming for the purpose more food 

 than usual — or if this is not forthcoming, consuming a part of its 

 own reserve of adipose tissue — so that from this source fresh com- 

 plications of the problem arise. 



The labor and ingenuity with which all these difficulties have 

 been encountered is certainly worthy of the highest praise, and I 

 willingly admit the probably approximate truth of the figures 

 generally in use, say 2J to 2f million gramme-degrees as the daily 

 average heat-production of an adult man, and 150,000 to 200,000 



