CLIMATOLOGY 



1419 



Climatology. — ^At the present moment the so-called endemic regions 

 are an area in the Kurdistan Hills, with a secondary area in Irak, 

 in Mesopotamia; another area about the Himalayas — i.e., Kumaon 

 and Garhwal, in India, Thibet and Yunnan, in China — and four 

 lesser areas — viz., Benghazi, in Tripoli, Uganda, in Central Africa, 

 Azeer, in Arabia, and the trans-Baikal Province of Siberia — but only 

 the first two are of real importance as far as we know. On the 

 strength of these two different regions an attempt has been made 

 to differentiate two distinct types of the disease: the first, the 

 Western Asiatic, being mild, and pneumonic cases rare, while it is 

 often self -limited, not capable of wide distribution, and not asso- 

 ciated with an epizootic in rats; the second is the Indo-Chinese 

 plague, or the disease as it is known to-day. It seems, however, 

 hardly likely that such a distinction will be supported when the 



disease in the first area is 



carefully studied. Climate 

 appears to have but little 



influence on the distribution | ' t 



of the disease, and soil appar- , 

 ently none. In India an ex- 

 cessive rainfall seems to favour , 

 the spread and virulence of 

 the malady. The hot season ■ 

 of the tropics and the winter 1 J, 



season of the Temperate Zone • * ''"'A,; \, 

 are deleterious to the spread 

 of the disease. The reason for 

 this appears to be the effect of 

 temperature on the bacilli in 

 the flea, which disappear 



rapidly from its stomach above Fig. 669.— Plague Bacilli in the 



70° F. they are virulent. 

 Moreover, as has already been stated in the chapter on Fleas, high 

 temperatures restrain the adults from laying eggs and the larvae from 

 developing. When temperatures below 50" F. are reached, it is found 

 that rats die before the bacilli pass into the blood, and therefore the 

 fleas do not become infected when sucking the blood. A temperature 

 of about 70° F. is therefore best for the propagation of an epidemic. 



etiology {vide also pp. 909 and 943). — The aetiology of plague 

 has been placed on a sure footing by the labours of Kitasato, 

 Yersin, Cantlie, Simpson, Thompson, Ogata, KoUe, Martini, and 

 the Special Committee already mentioned, together with the Second 

 Indian Commission. 



It is caused by the Pasteur ella pesiis (usual name: Bacillus pestis) 

 of Kitasato and Yersin, which is found in the fluid of the initial 

 cutaneous vesicle, the buboes, the spleen, the blood, and the sputum 

 in cases of pneumonia. When inoculated into monkeys, cats, rats. 



85° F., and are very ineffectual 

 at that temperature, while at 



Blood, (X 1,000.) 

 (From a photograph by J. J. Bell.) 



