554 Plague 



willingly, bite men. By placing guinea-pigs in cages upon the floor 

 of the infected houses, the fleas of all kinds quickly attack them 

 with resulting infection, but if the guinea-pigs are kept in flea- 

 proof cages, or if the cages are surrounded by " tangle-foot," or 

 "sticky fly-paper," the fleas, not being able to spring over the 

 barrier, are caught on the sticky surf aces and do not reach the guinea- 

 pigs, which then remain uninfected. What is true of the guinea- 

 pigs is undoubtedly true of the rats; the disease is transmitted from 

 rat to rat by the fleas. When the rats die, the fleas being hungry, 

 jump upon any convenient warm-blooded animal to satisfy their 

 appetites, and when human beings become their victims, infection 

 may follow the bites. It is now clearly demonstrated that though 

 Pulex irritans, the human flea, prefers to bite human beings, and 

 Xenopsylla cheopis, the rat flea, prefers to bite rats, under stress of 

 necessity preferences are set aside and miscellaneous feeding prac- 

 tised by these and probably all other fleas. 



A peculiar circumstance attending flea infection has been discovered 

 by Bacot and Martin* who find that when Xenopsylla cheopis and 

 Ceratophyllus fascia tus are fed upon septicemic plague blood, the re- 

 spective fleas suffer from a temporary obstruction at the entrance 

 of the stomach, caused by a massive growth of the plague bacilli. 

 This culture appears to start in the intercellular recesses of the 

 proventriculus and grows so abundantly as to choke this organ and 

 extend into the esophagus. Fleas in this condition are not 

 prevented from sucking blood, as the pump is in the pharynx, but 

 they only succeed in distending an already contaminated esophagus, 

 and on the cessation of the pumping act, some of the blood is 

 forced back into the wound. Such fleas are persistent in their 

 endeavors to feed and this renders them particularly dangerous. 



Bacotf found that infected fleas remained infectious when 

 starved for forty-seven days, and that when they were subse- 

 quently permitted to feed upon mice, another period of twenty 

 days might supervene before the mice became infected. 



The cutaneous and subcutaneous inoculation in man is followed 

 by lymphatic invasion with bubo formation. Beyond this lymphatic 

 barrier but few bacilli get so that in the greater number of cases 

 with buboes there is little blood infection. However, should the 

 bacilli be highly virulent or the patient exceptionally susceptible, 

 the septicemic form of the disease may supervene, and the case 

 progress to a rapidly fatal termination. 



Intravenous and Intraperitoneal Inoculations produce rapidly fatal 

 septicemic forms of plague. 



KleinJ found that intraperitoneal injection of the bacillus into 

 guinea-pigs was of diagnostic value, producing a thick, cloudy, 



"The Journal of Hygiene," Plague Supplement, in, 1914, p. 423. 

 t" Journal of Hygiene," Plague Supplement, No. rv, Jan., 1915, p. 770. 

 j "Centralbl. f. Bakt. u. Parasitenk.," xxi, No. 24, July 10, 1897, p. 849. 



