INFLUENCE OF ATMOSPHERIC TEMPERATURE. 161 



mean humidity of 81 \0; durinj? January, 1904, a mean daily 

 temperature of 29''. 1 F. and a mean humidity of SS^.O; during: 

 February, 1904, a mean daily temperature of 36°. F. and a 

 mean humidity of 85°. O." 



Therefore the conditions were such that droplets of sputum 

 suspended in the air would have had a tendency to evaporate 

 to dryness only with extreme slowness. 



Gill ' appears to have been the only investigator who has 

 devoted especial attention to the epidemiology of pneumonic 

 plague in India. He says: 



Pneumonic plague presents well-marked features as regards its time of 

 occurrence, which cannot be considered altogether accidental and without 

 significance. 



In the four epidemics of which I have notes the time of its first appear- 

 ance was as follows: 



1905-1906 Epidemic (Sept.-Sept.) Jan. 24th, 1906. 

 1906-1907 " " Feb. 1st, 1907. 



1907-1908 " " Dec. 13th, 1907. 



1908-1909 " " Oct. 10th, 1908. 



The last outbreak in the 1907-1908 epidemic was on March 16th, and 

 in the two former epidemics this was noted as about the time of the last 

 outbreak and its occurrence after April 1st has not been noted. 



The characteristic of pneumonic plague is therefore its occurrence at 

 the early part of the plague season, during the months of January, Feb- 

 ruary, and March, that is, while the epidemic is on the increase but before 

 it has reached its maximum intensity. 



Thus, while in the Punjab, the time of maximum intensity is April and 

 the beginning of May pneumonic plague is chiefly prevalent in February. 



But not only is this the case, but it exhibits the same features in regard 

 to its time of occurrence in the individual epidemics in villages. 



For as was exemplified in regard to the typical case of Mokal it was at 

 the commencement of the epidemic that it appeared and it lasted a com- 

 paratively short time, being succeeded or replaced by a more prolonged 

 bubonic outbreak. 



It is not easy to understand the reason for this, but it suggests that the 

 organism of plague has acquired at this time an unusual or perhaps "ex- 

 alted" degree of virulence which, however, it is not long able to maintain. 



I am unable to give any figures showing the actual prevalence of the 

 disease or even to roughly estimate the proportion it bears to the general 

 epidemic. 



Judging from reports one reads it is probable that it varies in different 

 parts of India, and it is my impression that it is commoner in the compara- 

 tively cool climate of the Punjab than in the warmer and moister parts 

 of India. 



' These data are taken from observations made at 10 a. m. and 4 p. m. 

 The 8 a. m. temperatures and humidity for the same months are: Dec, 

 1903, 28°.9 and 92°.0, respectively; Jan., 1904, 28°.4 and 93°.0; Feb., 1904, 

 33M and 90°.0. 



* Indian Med. Gaz. (1909), 44, 135. 



105936 3 



