THE EXTERNAL ENVIRONMENT 231 



The excitability of the nerves increase at temperatures from 

 up to 40 C., so that a rise of temperature is felt more parti- 

 cularly in the nervous properties^ 1 ) the movements of man. 



A very hot day in Paris, for example, is distinguished by the 

 same effects on the people as in a tropical town. This was the 

 case in July and August, 1911. 



168. Temperature retards or accelerates the respiration accord- 

 ing to whether it is high or low. The gaseous exchanges which 

 increase with the lowering of the temperature, ( ? ) are due to the 

 increasing intensity of the combustions. 



Intense heat increases the rhythm of the respirations, and 

 gives rise to a veritable palpitation (Richet). It is seen in dogs 

 when they pant in the sun. It causes profuse perspiration, ( 3 ) 



The gaseous exchanges, within certain limits of temperature, 

 are easier when the external environment is cold ; the cold air 

 penetrates the pulmonary membrane by a sort of thermo- 

 endosmosis, towards the warmer surrounding matter. ( 4 ) In 

 addition, it contains more oxygen than the same volume of hot 

 air, which is a favourable condition for the economical expendi- 

 ture of the organism. 



Respiration in an overheated atmosphere is therefore unfavour- 

 able to physiological labour. In regard to the discomfort due to 

 high temperatures Coulomb made some observations on the work 

 carried out by French soldiers in Martinique. ( 5 ) He concluded that 

 in such a tropical climate, where exertion caused profuse per- 

 spiration, the daily output of work was less than half that which 

 could be effected in a temperate climate. ( 6 ) 



169. When the temperature exceeds certain limits, the 

 organism suffers. Extreme cold demands intense calorific pro- 

 duction to maintain the internal temperature constant, while 

 excessive heat induces profuse perspiration. 



In inhabited countries the extremes of the average monthly 

 temperature rarely exceed + 36 C. and 22 C. The variation 

 is at the outside 60 C. In Europe and Northern Africa the 

 greatest cold only reaches 14 C., and the most intense heat 

 -f 36 C. Such temperatures do not trouble the physiological 



(*) G. Weiss (Journal de Physiol., 1903, p. 31). 

 ( a ) Vernon (Journal of Physiol., 1897, p. 443). 



( 8 ) Ch. Richet (Dictionnaire of Richet, article Chaleur, vol., iii., p. 175) ; 

 Langlois and Garrelon (Journ. de Physiol., 1906, p. 236, 1907, p. 640). 



( 4 ) G. Lippmann (Comptes Rendus Acad. Sciences, vol. cxlv., p. 104, 

 1907) ; Aubert, Thesis for Doctorate, Paris, 1912). 



( 5 ) Coulomb (memoire quoted, end) 1785 (date of publication). 



(') The real average temperature of Martinique is 25'60, a maximum of 

 27 and a minimum of 24. It must be added that the natives of hot 

 countries surfer less from the high temperature than strangers ; (see 171). 



