ENTOMOLOGY

CHAPTER VIThe Relations of Climate and Life and Their Bearings on the Study ofMedical Entomology.lW. Dwight PierceAll animal and plant life has its being and reacts according to defi~'Ilite laws in which we find the climatic factor of primary importance.We cannot go far into a subject with as many inter-relationships asmedical entomology without finding it necessary to know something ofthe climatic laws which govern the lives of the various organisms concerned.In several of the lectures attention is especially called to apparentdiscrepancies in the interpretation of climatic effects on the life of theinsects, and this is particularly true in case of the lice. Throughoutour literature there is to be found a hazy notion of the importance oftemperature and still haz~er 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 themost important principles as now understood.On a proper understanding of the relations of temperature andhumidity to the life and development of insects, animals, and diseaseorganisms, depend all transmission experiments, all efforts in keepingalive the various creatures involved, all interpretations of results andmany practical measures of control.This difficult subject will be stated in as simple language as possibleso that all may see the basic principles at least.Everyone of us knows that cold and heat can cause pain. We haveindeed a clear understanding that cold and heat kill. We recognize thefact that we seem to work best under conditions when we are absolutelyoblivious of heat or cold, dryness or moisture. We have felt stupidin murky weather. We have felt parched and dried from extremelydry weather. In other words, we cal). now recognize four conditionswhich may affect our well-being, cold, heat, dryness, moisture. These('an be expressed on two scales-temperature and relative humidity. Inother words, we should be able to chart our own susceptibilities to thesefactors by running, for example, a temperature scale vertically on our1This lecture was read July 1, 1918 and issued the same day.07