196 FOODS AND DIETARIES 



The experiments of Atwater with the respiration calorimeter should be explained 

 and pictures of the apparatus shown so that the pupils may be impressed with the 

 delicacy and magnitude of the experiments. This respiration calorimeter is de- 

 scribed by Professor Atwater as follows : 



"Its main feature is a copper- walled chamber 7 feet long, 4 feet wide, and 6 feet 

 4 inches high. This is fitted with devices for maintaining and measuring a ventilat- 

 ing current of air, for sampling and analyzing this air, for removing and measuring 

 the heat given off within the chamber, and for passing food and other articles in and 

 out. It is furnished with a folding bed, chair, and table, with scales and appliances 

 for muscular work, and has telephone connection with the outside. Here the sub- 

 ject stays for a period of from three to twelve days, during which time careful 

 analyses and measurements are made of all material which enters the body in the 

 food, and of that which leaves it in the breath and excreta. Record is also kept of 

 the energy given off from the body as heat and muscular work. The difference 

 between the material taken into and that given off from the body is called the bal- 

 ance of matter, and shows whether the body is gaining or losing material. The 

 difference between the energy of the food taken and that of the excreta and the 

 energy given off by the body as heat and muscular work is the balance of energy, 

 and if correctly measured, should equal the energy of the body material gained or 

 lost. With such apparatus it is possible to learn what effect different conditions 

 of nourishment will have on the human body. In one experiment, for instance, the 

 subject might be kept quite at rest, and in the next do a certain amount of muscular 

 or mental work with the same diet as before, then by comparing the results of the 

 two, the use which the body makes of its food under the different conditions could 

 be determined ; or the diet may be slightly changed in the one experiment, and the 

 effect of this on the balance of matter or energy observed. Such methods and 

 apparatus are very costly in time and money, but the results are proportionately 

 more valuable than those from simpler experiments." 



The experiments of Chittenden should also be explained. - (See 

 Chittenden's Nutrition of Man.) 



Atwater's Calorimeter. (See diagram on page 197.) 

 Atwater's respiration calorimeter, an apparatus for determining the income and 

 outgo of energy, and respiratory products of the human body, under varying con- 

 ditions, consists of an air-tight copper chamber, insulated from the surrounding 

 air by a zinc casing and three wooden ones, with dead-air spaces between. It is 

 provided with a door and a window for the introduction and removal of food. 

 Closely attached to the outside of the copper wall are 304 thermoelectric couples 

 (A) which, electrically, report the temperature of the calorimeter chamber to the 

 observer's table (B). The temperature of the chamber is maintained as nearly 

 constant as possible by a current of cold water, pumped by the electric pump 

 (O through the cooling tank (D) to (E), where its temperature is taken just before 

 it enters the large-surface, winged pipes around the chamber. When the water 

 emerges at (F), its temperature is taken again and its volume and flow measured 

 at the water meter (GO before it returns to the pump. From these data, knowing 

 the rise in temperature and the amount of water so raised, the amount of heat 

 developed within the calorimeter may be computed. The flow of water may be 

 regulated so as to carry off any amount of heat developed. 



