ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



41.9 



BaciJJus coU. Some members of the group are motile, others are non- 

 motile. ]\[ost of them ferment glucose and lactose with production of 

 gas, and thus bear a close resemblance to B. coU. The following table 

 clearly shows the affinities of the group with dysentery bacilli on the one 

 hand, and with B. coU on the other. 



Non-motile Pseudo-dysentery Bacilli. Agglutinations. 



Saturation Deficiency and Temperature in relation to Plague.* 

 E. St. John Brooks has studied the combined eff'ect of saturation 

 deficiency and of temperature on the course of epidemic plague, and 

 has come to the conclusion that in the majority of cases they exert 

 an influence on the course of the disease. Under certain conditions, 

 however, plague epidemics come to an end when the climatic conditions 

 are presumably favourable for a continuance of infection. In these cases 

 other factors must come into play, such as the seasonal breeding of rats, 

 the decrease in the number of rats during epidemic periods, and the 

 accompanying increase in the proportion of immune to susceptible rats. 

 The adverse influence of high temperature and saturation deficiency 

 may be explained by their effect on the duiation of life of the rat- flea, 

 Xenopsylla clieopis, when separated from its host. When the mean tem- 

 perature rises above 80° F., and when such rise is accompanied by an 

 increase in the saturation deficiency to above • 30 of an inch, plague 

 cannot maintain itself in epidemic form, though a high temperature 

 per se may not bring about the termination of a plague epidemic. 

 Many examples can be adduced of plague epidemics coming to an end 

 when the temperature remains well below 80° F., and in such cases the 

 determining factor appears to Ije the rising of the saturation deficiency 

 to over • 30 of an inch. 



* Journ. Hyg. Plague, Suppl. v. (1917) pp. 881-99. 



