PLAGUE 461 



Macacus sinensis, Semnopithecus entellus, Macacus nemestrinus in the Bombay 

 Zoological Gardens (Indian Commission) ; in cats in the Azores (de Souza, Arruda 

 and Pinto) ; in ground-squirrels Citellus beccheyi in America (M'Coy) ; and in 

 brush rats Neotoma (M'Coy). The disease is also believed to occur in the mar- 

 mot Arctomys bobax (vide infra). The infection of the ground-squirrels on the 

 Pacific Coast of the United States of America was believed to be the source of 

 infection in a number of cases of plague in that district. ] 



During epidemics of plague a large number of animals [other than those men- 

 tioned have been said to be] affected at the same time as man : [Simpson, for 

 example, stated that pigs, calves, buffaloes, sheep, hens, ducks, geese, turkeys 

 and pigeons are susceptible. But Bannerman and Kapadia, as Members of the 

 Commission appointed by the Advisory Committee, failed to infect pigs, calves, 

 fowls, turkeys, geese and ducks, and showed that buffaloes are not susceptible. 

 The conclusions of the Indian Commission are supported by many other observers 

 among whom may be mentioned Pearse in Hong-Kong, London in Russia, Watkins- 

 Pitchford in Natal and de Souza, Arruda and Pinto in the Azores. The last named 

 observers further showed that dogs are practically refractory to plague and that 

 ferrets are only susceptible to large doses of the virus. From these and other facts it 

 appears, as Bannerman points out, that Simpson confused the plague bacillus with 

 the hog-cholera bacillus (p. 438) and with the bacillus of fowl cholera (p. 447).] 



Plague is transmitted from rat to rat and from rat to man by fleas (Simond). 

 [The rat flea, Xenopsyllus (Pulex ) cheopis Rothschild, under certain circumstances 

 is attracted by man and will readily bite and feed on him (Advisory Com- 

 mittee). 1 ] 



[It is possible to transmit plague by means of Pulex irritans. Nevertheless the 

 direct transmission of the. disease from man to man cannot, at the present time, be 

 of frequent occurrence or we should have evidence of direct infection instead of 

 dependence upon the epizootic. The reason why the human flea is ineffective is 

 because in human cases the average degree of septicaemia before death is so much 

 less than in rats that the chance of a flea imbibing even a single bacillus is small 

 (C. J. Martin).] 



Rats suffering from plague are a ready prey to fleas and plague bacilli have been 

 found in the stomachs of these insects. If a flea be taken from a plague-infected 

 rat, crushed in a mortar and inoculated into a mouse, the latter becomes infected 

 with plague [Ogata]. 



[There is good evidence that the plague bacillus multiplies in the stomachs of 

 fleas (Indian Commission).] 



[Simond holds that when a flea bites man or the lower animals it discharges the 

 contents of its intestine near the bite ; should the flea be infected the plague bacillus 

 which will be present in the excreta will be rubbed into the bite by the scratching 

 induced as a result of the bite. The experiments of the Advisory Committee would 

 appear to support this view. Both male and female fleas bite.] 



A healthy rat coming in contact with fleas from a plague-infected rat dies of 

 plague. When a rat dies the fleas leave the carcase. 



Plague is similarly transmitted by fleas from man to man. In the early stages 

 of an infection with the plague bacillus small inflamed areas are occasionally seen, 

 varying in size from a pin's head to a walnut, transparent at first then purulent and 

 always containing bacilli. These inflammations are found on parts exposed to the 

 bites of insects, and it would appear that they mark the sites of inoculation. Sticker, 

 working in Bombay, pricked himself with an infected instrument and after 3 days 

 an inflammation appeared at the site of the injury and symptoms of plague manifested 

 themselves. 



[* Xenopsyllus cheopis is, except in Northern and Central Europe, the commonest flea 

 found on house and port rats all over the world and in some localities is almost the only 

 flea found. Ceratophyllus fasciatus is the flea usually found on Mus decumanus in Great 

 Britain (M. rattus is a rare animal in the British Islands), and this is also the case, apparently, 

 throughout Northern and Central Europe (Rothschild). 



[X. cheopis is identical with P. pallidus Taschenberg, with P. murinus Tiraboschi 

 and with P. philippinensis Hertzog. 



[P. irritans, the flea commonly found on man, Ctenocephalus canis, of dogs, cats, etc., and 

 Ctenopsyllus musculi, the common house mouse flea, have occasionally been found on 

 rats.] 



