842 ANIMAL HEAT. 



artificially maintained at the normal height. 1 These experiments have 

 been extended by PHliger, 2 who found in curarised rabbits that the 

 intake of oxygen and the output of carbon dioxide fell respectively to 

 3 5 -2 and 374 per cent, of the normal exchange : a rise in the tempera- 

 ture of the surroundings caused an increase in the respiratory exchange, 

 a-nd 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 Colasanti 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 which 

 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 Lowy 8 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 



equivalent of heat would give - =103,000 calories. Foster 10 cal- 



culates that the work done by the heart is nearly 60,000 kilogrammetres, 



1 Zuntz, Arch.f. d. gcs. Physiol., Bonn, 1876, Bd. xii. S. 522. 

 z Ibid., 1878, Bd. xviii. S. 255. 

 * Ibid., 1878, Bd. xvi. S. 157. 



4 Rumpf, ibid., 1884, Bd. xxxiii. S. 538; Pembrey, " Proc. Physiol. Soc.," Journ. 

 Physiol., Cambridge and London, 1894-1895, vol. xvii. 



5 " Goulstonian Lectures," Lancet, London, 1887, vol. i. p. 558. 



6 Beclard, Arch, de med. nav., Paris, 1861, pp. 24, 157, 257. 



7 Richet, Compt. rend. Soc. de biol., Paris, 1892, p. 896. 



8 Arch.f. d. yes. Physiol., Bonn, 1889, Bd. xlv. S. 625 ; and 1890, Bd. xlvi. S. 189. 



9 "Phys. Med.," 1869, p. 229. 



10 "Text-Book of Physiology," 1891, 5th edition, pt. 1, p. 254. 



