METHODS OF INVESTIGATION. 247 
crude forms of the air-calorimeter. In 1885 Richet * described an 
air-calorimeter for small animals, the heat being measured by the 
increase in the volume of a confined portion of air at constant press- 
ure. His experiments were of short duration (1 to 14 hours) and 
no specific statement is made regarding ventilation and no mention 
of any determinations of the latent heat of the water vapor. 
In 1886 d’Arsonval ¢ described a differential air-calorimeter, 
and in 1890 { two other forms of animal calorimeter, the first being 
a water-calorimeter of constant temperature with automatic regu- 
lation of the flow of water, for which a high degree of accuracy is 
claimed, and the second an air-calorimeter, but he reports no ex- 
periments with either form. In the same year Laulanié § (see p. 70) 
described briefly a Regnault respiration apparatus which was also 
used as a calorimeter, and has subsequently reported some results 
obtained by its use. 
One of the best known forms of animal calorimeter is that of 
Rubner.|| This is essentially a Pettenkofer respiration apparatus, 
the walls of the chamber being double and the whole surrounded 
by an air space which in its turn is surrounded by a jacket con- 
taining water kept at a constant temperature. The amount of 
heat given off to the calorimeter is measured by the expansion 
under constant pressure of the confined volume of air between the 
two walls of the respiration chamber, while from comparative de- 
terminations of moisture in the ingoing and outcoming air the heat 
removed in the latent form is computed. 
Rosenthal 4 has constructed a somewhat similar instrument in 
which the respiratory portion is a Regnault apparatus, while the 
heat is measured by the increase in pressure of the air at constant 
volume, instead of by the increase in its volume as in Rubner’s 
apparatus. Both instruments are therefore air-calorimeters, and the 
numerical values of their readings must be determined experimen- 
tally for each instrument. These two forms of apparatus are of a size 
sufficient for experiments with small animals (rabbits or small dogs). 
* Archives de Physiol , 1885, II, 237. 
+ Jour. de l’Anat. et Physiol., 1886. 
t Archives de Physiol., 1890, pp. 610 and 781. 
§ Ibid., p. 571. 
|| Calormetrische Methodik, Marburg, 1891; Zeit. f. Biol., 80, 91. 
4 Arch. f. (Anat. u.) Physiol., 1894, p. 223. 
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