INTERNAL WORK. 371 
and others, computes the heat production per unit of surface, and 
also compares it with the amount of nitrogen computed to be 
present in the organs of the animal on the several days of the ex- 
periment. The following results of one of Rubner’s experiments 
with rabbits are typical of those obtained in this way: 
Heat Production per Day. 
eas 
Day of Fasting. Weiaht, ge Per 100 
Grms. Total, | Per Kg.. | Meter of | Nitrogen, 
als. Cals. Surface, Cals. 
Cals. 
Third Salhi Sa ane eee gisy eats 2185 155 71.0 730 310 
Pifth 3 spa phen oF de eee 2093 117 55.9 556 243 
Seventh Sia bd aya aoe Atta Mea Blee ate ek 2007 102 50.8 499 220 
INH GH Ss. acc52e-s acsceea are aged aan 1923 97 50.5 488 221 
Tenth and twelfth ......... 1841 95 51.6 494 227 
Thirteenth and fourteenth ..| 1735 88 50.7 463 222 
Fifteenth and sixteenth ....| 1646 81 49.2 452 218 
Seventeenth and eighteenth] 1507 72 47.8 428 219 
The heat production per unit of surface is seen to decrease at 
first rapidly and later more slowly, while the heat production per 
unit of weight shows but a slight decrease and that per unit of 
nitrogen scarcely any. From these and other similar results, Voit 
concludes that the law of the proportionality of heat production to 
surface as enunciated by Rubner and as extended by himself must 
be limited in its application to animals in like bodily condition, 
and that an animal with a low stock of nitrogenous tissue will, 
under the same conditions, show a lower heat production per unit 
of surface than-a well-nourished animal. The exceptionally low 
average for the rabbit noted on p. 369 he explains on this hypoth- 
esis as resulting from the frequent use for such experiments of 
animals in a poorly nourished and “degenerate” condition re- 
sulting from long confinement. 
The result has an interesting bearing in another direction. 
Most of the experiments cited by Voit were probably made at tem- 
peratures below the critical points for the several animals. In 
our previous discussion we have assumed that under these circum- 
stances the heat regulation is accomplished largely by “ chemical” 
means—by variations in the rate of production. In these experi- 
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