842 ANIMAL HEAT. 
artificially maintained at the normal height. 1 These experiments have 
been extended by Pftuger, 2 who found in curarised rabbits that the 
intake of oxygen and the output of carbon dioxide fell respectively to 
35 - 2 and 37*4 per cent, of the normal exchange : a rise in the tempera- 
ture of the surroundings caused an increase in the respiratory exchange, 
and in the temperature of the animal, whereas a fall in the external 
temperature produced the opposite effects. These phenomena were not 
due to diminished supply of oxygen, for artificial respiration was 
maintained, the heart beat strongly, and the venous blood was brighter 
than in the normal animal. Further, it is not due to poisoning of the 
muscle substance itself , for (Jolasanti 3 found that the oxidation in the 
muscles of a limb with an artificial circulation was the same whether 
the blood did or did not contain curari. Similar results have been 
obtained with anaesthetics and drugs which depress the activity of the 
nervo-muscular system. 4 
It will be shown later that section of the spinal cord or of the 
motor nerves reduces a warm-blooded animal to a cold-blooded condition ; 
its temperature falls, and it can no longer regulate its temperature. 
The completeness of the effect seems to depend upon the number of the 
muscles paralysed. On the other hand, calorimetric determinations 
show that muscular activity greatly increases the production of heat 
and the respiratory exchange. 
It has already been stated that young mammals and birds, in whicdi 
muscular co-ordination is well developed, are able to maintain their 
temperature at birth, whereas others born in a helpless condition 
resemble cold-blooded animals. 
According to D. Macalister, 5 the muscles are fatigued as producers of 
heat sooner than as producers of work, and the effect of cold upon the 
muscles of anaesthetised mammals is to markedly depress the thermo- 
genic function. 
The involuntary muscular contraction in shivering causes a rise 
of temperature, 6 and this is especially noticeable in small thin dogs 
with little fur : in fact, shivering must be looked upon as an involuntary 
protective mechanism against cold. 7 In man, as Ldwy s has shown, it 
may increase the metabolism by 100 per cent. The warming effect of 
muscular exertion is a matter of ordinary daily experience, and is well 
shown by the difference in the walk of a man during cold and hot 
weather. 
The heat produced by the contraction of the heart. — The work 
done by the human heart was estimated by Grehant 9 at 43,800 kilo- 
grammetres in twenty-four hours, and this according to the mechanical 
I q QflO 
equivalent of heat would give =103,000 calories. Foster 10 cal- 
424 
culates that the work done by the heart is nearly 60,000 kilogrammetres, 
1 Zuntz, Arch. f. d. ges. Physiol., Bonn, 1876, Bd. xii. S. 522. 
"Ibid., 187S, Bd. xviii. S. 255. 
-Ibid., 1878, Bd. xvi. 8. 157. 
4 Rumpf, ibid., 1884, Bd. xxxiii. S. 538; Peinbrey, " Proc. Physiol. Soc," Journ. 
Physiol., Cambridge and London, 1894-1895, vol. xvii. 
5 " Gonlstonian Lectures," Lancet, London, 1887, vol. i. p. 558. 
6 Beclard, Arch, de mid. nac, Paris, 1861, pp. 24, 157, 257. 
7 Richet, Compt. rend. Soc. de biol., Paris, 1892, p. 896. 
8 Arch. f. d. ges. Physiol., Bonn, 1889, Bd. xlv. S. 625 ; and 1890, Bd. xlvi. S. 189. 
9 "Phvs. M.6&.," 1869, p. 229. 
10 "Text-Book of Phvsiology," 1891, 5th edition, pt. 1, p. 254. 
