THE ECOLOGY OF BUBONIC PLAGUE. 



James Zetek, Ancon, C. Z. 



When I entered for the first time the office of the Chief 

 Sanitary Officer of the Isthmian Canal Commission, I saw a 

 large wall chart, the curve of which told exactly how much 

 malaria there was each month on the Canal Zone, expressed as a 

 percentage of the entire working force. This was six years ago. 

 This chart registered the splendid results obtained by the 

 sanitation corps of the I. C. C; it showed how, although the 

 working force was increased yearly, the malaria rate kept 

 declining yearly. Today malaria is practically exterminated. 



This curve showed me more than merely the results of 

 2Lnt\- Anopheles measures. It showed a definite, seasonal rise 

 and fall in the rate. Malaria was at its lowest from about 

 November or December until April or May, and reached its 

 crest in July. It was the lowest during the dry season, and 

 highest during the wet. Malaria began to shoot upward just 

 after the first heavy rains had fallen. When the dry season 

 approached, the rate fell rapidly. If the dry season was late in 

 coming, then malaria behaved accordingly. The critical factor 

 here is moisture. 



The bulk of this malaria is transmitted by Anopheles 

 albimaniis Wiede., and its racial variety tarsimaciilata Goeldi. 

 They breed extensively during the wet season. Field inspec- 

 tions show rapid increase in the number of breeding places just as 

 soon as the rains start in. During the dry season it is very 

 difficult to find larva? of these species. Instead of them, we 

 find plenty of A . pseudopunctipennis Theob., a species apparently 

 unimportant in the transmission of malaria on the Isthmus. 

 Albimaniis is a wet season species; pseudopunctipennis is a dry 

 season species. Maximum humidity, maximum malaria and 

 maximum numbers of transmitors of malaria coincide as to 

 time. 



In addition to this, it must be noted that the advent of the 

 first heavy rains means also that the workmen get wet, either 

 going to or from their work, or even while working. This 

 means a lowering of their bodily resistance, a factor which is 

 extremely important for the early rise of human malaria. 



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