WARM-BLOODED ANIMALS. 7 1 3 



feels cold, is not necessarily brought about by a conscious effort of the 

 will ; it is to a great extent reflex, and shows itself in the more energetic 

 performance of work, or, if no work be done, the reflex may become so 

 imperative as to give rise to involuntary movement, shivering, which is 

 only of value to the organism as a source of greatly increased heat 

 production. There is little doubt but that a normal man, who feels cold 

 and is free to follow the dictates of his sensations, will be more active, 

 and will produce more carbon dioxide and absorb more oxygen than he 

 would in warm surroundings. The man who suppresses increased 

 muscular action when he feels cold, is abnormal. It follows, therefore, 

 that man is no exception to the general rule that warm-blooded animals 

 in cold surroundings increase, in warm surroundings diminish, their 

 respiratory exchange and production of heat. 



It has already been shown that a rise or fall in external temperature 

 determines in the same direction a variation of the respiratory exchange 

 of cold-blooded animals. What, then, is the cause of the totally opposite 

 result observed in warm-blooded animals ? To this question only an 

 incomplete answer can be given. The difference is due to the nervous and 

 muscular mechanisms which maintain the fairly constant temperature 

 observed in the warm-blooded animals. For if, as Sanders-Ezn 1 and 

 Pfliiger 2 have shown, the exposure to cold be excessive, and the animal's 

 temperature falls to 26, then also there is a fall in the intake of oxygen 

 and the output of carbon dioxide ; on the other hand, if by means of 

 warm baths the internal temperature of the animal is raised above the 

 normal, then there is an increase above the average respiratory exchange. 

 In fact, a warm-blooded animal responds to a rise or fall in the tempera- 

 ture of its surroundings with a decrease or increase of its metabolism, 

 only as long as its internal temperature remains near the normal point. 

 Moreover, Pfliiger has proved the connection between the normal 

 response to a change of external temperature and the nervo-muscular 

 system, for he shows that a mammal paralysed with curari 3 or with its 

 spinal cord cut in the lower cervical region, absorbs more oxygen and 

 discharges more carbon dioxide in warm than in cold surroundings ; it 

 resembles in this respect a cold-blooded animal. A similar cold-blooded 

 condition can be produced in mammals, as Eumpf, 4 Eichet, 5 and 

 Pembrey 6 have observed, by exposing the anaesthetised animal to 

 changes of temperature. 



The objection that these experiments are associated with markedly 

 abnormal conditions, and therefore cannot indicate the true condition of 

 normal animals, is met by the fact that it is possible to trace the 

 gradual development of the means whereby an animal increases or 

 decreases its metabolism and maintains a fairly constant heat of its 

 body, notwithstanding wide variations in the temperature of its 

 surroundings. This has been shown by Penibrey 7 in a series of 

 comparative experiments upon full-grown and newly-born animals. In 

 the full-grown mouse the response to a change of external temperature 



1 Ber. d. Jc. sacks. Gesdlsch. d. Wissensch. Math.-phys. KL, Leipzig, 1867, S. 58. 

 - Arch.f. d. ges. PhysioL, Bonn, 1878, Ed., xviii, S. 247. 



3 See also Zuntz, Arch. f. d. ges. PhysioL, Bonn, 1876, Bd. xii. S. 522. 



4 Ibid., 1884, Bd. xxxiii. S. 538. 



5 ,Oompt. rend. Acad. d. sc., Paris, 1889, tome cix. p. 190. 



6 "Proc. PhysioL Soc.," Journ. PhysioL, Cambridge and London, 1894-95, vol. xvii. 



7 Journ. PhysioL, Cambridge and London, 1894, vol. xv. p. 40i ; 1895, vol. xviii. 

 p. 363. 



