CHAPTER VI 



The Relations of Climate and Life and Their Bearings on the Study of 



Medical Entomology.^ 



W. Dwighf Pierce ^ 



All animal and plant life has its being and reacts according to defi- 

 nite laws in which we find the climatic factor of primary importance. 

 We cannot go far into a subject with as many inter-relationships as 

 medical entomology without finding it necessary to know something of 

 the climatic laws which govern the lives of the various organisms con- 

 cerned. 



In several of the lectures attention is especially called to apparent 

 discrepancies in the interpretation of climatic eff'ects on the life of the 

 insects, and this is particularly true in case of the lice. Throughout 

 our literature there is to be found a hazy notion of the importance of 

 temperature and still hazier notions of humidity. There is a great' 

 deal about these factors which help to govern life, that no one knows, 

 but it will pay us to have a clearly defined statement of some of the 

 most important principles as now understood. 



On a proper understanding of the relations of temperature and 

 humidity to the life and development of insects, animals, and disease 

 organisms, depend all transmission experiments, all efforts in keeping 

 alive the various creatures involved, all interpretations of results and 

 many practical measures of control. 



This difficult subject will be stated in as simple language as possible 

 so that all may see the basic principles at least. 



Every one of us knows that cold and heat can cause pain. We have 

 indeed a clear understanding that cold and heat kill. We recognize the 

 fact that we seem to work best under conditions when we are absolutely 

 oblivious of heat or cold, dryness or moisture. We have felt stupid 

 in murky weather. We have felt parched and dried from extremely 

 dry weather. In other words, we can now recognize four conditions 

 which may affect our well-being, cold, lieat, dryness, moisture. These 

 can be expressed on two scales — temperature and relative humidity. In 

 other words, we should be able to chart our own susceptibilities to these 

 factors by running, for example, a temperature scale vertically on our 

 ^This lecture was read July 1, 1918 and issued the same day. 



07 



