51(> PHYSIOLOGY. 



closed by powerful iron screw clamps. In front of the door is a mat- 

 tress of sawdust several inches thick. Over and around the calori- 

 meter, instead of the usual sawdust or felt, I used the packing mate- 

 rial of wood-fiber known as excelsior. The whole instrument is 

 inclosed within a box which has a door. 



The calorimeter is sixteen inches in length and twelve inches 

 in diameter. The instrument has a circular opening through which 

 a thermometer graduated to one-fiftieth of a degree Fahrenheit passes 

 into the water. An opening is also provided in the air-tube into 

 which a thermometer can be inserted. 



This instrument is fairly exact. By calculation it is found that 

 the error is 5.4 per cent. After the performance of numerous experi- 

 ments it was found that the variations from this number were within 

 1 per cent. Hence it may be assumed that this is an instrument of 

 precision. For absolute accuracy the moisture of the air and the 

 barometric correction should be made,, but they would not alter the 

 result very perceptibly. The instrument is always used with the air 

 a degree or so above the temperature of the calorimeter. The agi- 

 tator is set in motion for a half-hour before the observation is com- 

 menced. The room temperature for twenty-four hours previously is 

 kept the same. With these precautions the instrument works ac- 

 curately. 



By the calorimeter we are enabled to measure the transforma- 

 tion of the potential energy of the food into heat and, at the same 

 time, measure the number of heat units produced. The total amount 

 of energy present in the human body might be measured by com- 

 pletely burning an entire human body in a calorimeter. By this 

 means it may be determined how many heat units are produced when 

 it is reduced to ashes: 



If a man were not supplied with food he would lose fifty grams 

 of his body-weight every hour. This is due to the constant oxidation 

 which occurs, whereby the materials of the body unite with the in- 

 spired and circulating oxygen to produce combustion and heat. 



It is known that any given oxidation will always produce the 

 same amount of heat. Thus, if a gram of fat be burned in a calorim- 

 eter there will be produced a certain and almost unvarying number 

 of heat units. By numerous experiments upon foodstuffs it has been 

 determined by the calorimeter just the number of heat units a gram 

 of each will yield. Just as in the calorimeter, only far more slowly, 

 are the foodstuffs within our bodies burned up. That is, the presence 

 of oxygen transforms the potential energy within them into kinetic. 



