i2 4 AIDS TO BACTERIOLOGY 



Norwegian species, and finally, the least susceptible of 

 all, our own common sewer rat.* In the Bombay district, 

 a new outbreak first attacks M us decumanus (the grey 

 sewer rat), passing to M us rattus (the black house rat), 

 and then on to man. The disease is largely spread by 

 fleas. On the death of an animal the fleas desert it for a 

 living host. The common rat-flea found in the tropics 

 (Xenopsylla cheopis) readily attacks man, and laboratory 

 experiments show that, provided a healthy animal can be 

 protected against the fleas of one that is plague-stricken, 

 the former is not likely to develop the disease, in spite of 

 the proximity of the respective cages. (X. cheopis has 

 only been found once on English rats.) 



Sambon insists that in epidemic plague transmission 

 from man to man is more frequent than transmission 

 from rat to man. He believes that during a true epidemic 

 the rat strain of B. pestis is replaced in many cases by a 

 human strain, and the rat fleas are replaced by the fleas 

 of man, and by those of the cat and dog, which attack 

 man as well. Jordan states that cervical buboes are 

 most common when flea infection has occurred. 



Serum Treatment. A horse is inoculated intravenously 

 with a suspension of dead bacilli weekly for three months. 

 During the next three months living organisms are given. 

 Various reports have been given of the efficacy of serum 

 treatment. 



Anti-Plague Vaccine. The ' Haffkine prophylactic ' 

 is prepared by growing a virulent bacillus in nutrient 

 broth containing butter-fat. After a week the stalactite 

 growth (see p. 122) is detached by shaking, and the broth 

 reinoculated with the organism. By the time the medium 

 has been treated thus four or five times development 

 becomes slow and scanty. The culture is sterilised by 

 heating to 65 C. for one hour, and 0'5 per cent, of carbolic 

 acid added. The dose employed is about 2 -5 c.c., which 

 is injected subcutaneously. A second injection, given 

 a week after the first, increases the immunity. By the 

 use of the Haffkine prophylactic the incidence of the 

 disease is much reduced, and among the vaccinated who 

 contract the disease the mortality is much less than 

 among the unvaccinated. 



* ' The Bacteriology and Etiology of Oriental Plague' (Klein). 



