CLIMATE 993 



Africa, which is a health resort for man but the home of 

 pestilence for animals. It is not the climate which must 

 be blamed for this latter, but largely the existence of insect 

 life charged with pathogenic germs.* 



It is, however, undoubted that heat, cold, rain, and wind 

 may act as predisposing causes of disease, and we may 

 briefly glance at these as factors, and consider how they 

 operate. 



In hot climates there is less tissue change occurring, and 

 in consequence less urea and carbonic acid are excreted, 

 while there is a freer action of the skin and less urine! 

 The heated air owing to expansion contains less oxygen, 

 and the number of respirations is increased in order to 

 compensate for this. The extremely active condition of 

 the skin is part of the cooling mechanism, and prevents 

 the blood rising to the temperature of the air ; the effect 

 of long-continued heat, especially in the absence of air 

 movement, becomes very trying, and with man heat-apoplexy 

 may under these conditions occur. There is nothing corre- 

 sponding to this in animals, excepting when they are perform- 

 ing labour : severe exertion plus a high external tempera- 

 ture with especially no movement of the air, may then easily 

 cause death. This is probably brought about by want of 

 proper oxygenation of the blood in an atmosphere largely 

 expanded by heat. During hot weather the body tempera- 

 ture rises considerably during work, but falls with cessation 

 of labour. 



In the absence of work the direct rays of the sun have 

 no action on the central nervous system of any equine or 

 ruminant ; but in animals new to hot countries the body 

 temperature may rise, and a condition of fever be produced 

 from standing exposed to the sun. The temperature will 

 also rise if acclimatized animals are left standing in a hot 

 sun, but with them it does not appear to be pathological. 



Animals, especially until acclimatized, feel the sun and 

 seek every opportunity for obtaining shade ; but that in 



* In this chapter the term insect is used in its convenient and not 

 necessarily zoological sense. 



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