125 



We have no record of plague bacilli having been demonstrated in 

 mites commonly found on rats, but no doubt if search be made they 

 could be found after feeding on a septicaemic plague rat. These mites, 

 however, always confine themselves closely to their particular host 

 and are not known to bite man. The tiny itch mite (Notoedres alepis, 

 Railliet and Lucet) producing rat scabies has, according to Schumann, 

 (2) been known to cause a cutaneous lesion in man, but this mite 

 need not be considered from a plague standpoint. 



The flea, on the other hand, lives -but part of the time on its host, 

 its eggs developing m the nests or runs of the animal. Again, this 

 insect does not confine itself to one particular species of host only, 

 as frequently the flea of one animal is found on an animal of an en- 

 tirely different species. Unlike the lice, they are very active and can 

 readily move from place to place. Not only that, but it has been 

 fi-equently demonstrated that the fleas of rats and of other animals 

 would readily take to man, especially if their natural host was 

 scarce. That rat fleas will bite man has been demonstrated by 

 Gauthier and Raybaud, working with the Leomopsylla cheopis; 

 Tidswell, Loemopsylla cheopis and CeMtopJiyllus fasdatus; Liston, 

 LoemopsyUa cheopis; Tiraboschi, Loemopsylla cheopis; Indian Plague 

 Commission, Loemopsylla cheopis; and McCoy and Mitzmain (3), 

 Loemopsylla cheopis, CeratophyUus fasdatus, and Gtenopsyllus muscvM. 

 It has generally been considered that the Ctenopsyllus musculi, 

 above all others, would not bite man, but the last-named observers 

 showed that it would occasionally feed, although it would not live 

 long, in captivity. One of the fleas, a CeratophyUus fasdatus, was 

 kept alive by Mitzmain for over four months on man's blood alone. 



EXPERtMENTS PROVING THAT FLEAS CAN TRANSMIT PLAGUE. 



By a series of experiments carried out in specially constructed 

 cages and godowns where healthy rats in the absence of fleas were 

 brought in contact with plague-infected rats, the Indian Plague Com- 

 mission showed that the healthy rats would not contract the disease, 

 notwithstanding the fact that they were not only in intimate contact 

 with the sick rats, but also with the contaminated food and excreta 

 of the sick rats. They then showed that if fleas were introduced the 

 heialthy rats would contract plague, the rate of progress of the epi- 

 zootic being in direct proportion to the number of fleas present. By 

 hanging cages containing healthy rats in cages holding infected rats, 

 but above the jumping distance of a flea, it was shown that the 

 healthy rats would remain well, while those in cages hung within 2 

 inches from the ground would contract plague. Thus they excluded 

 aerial infection. They also found that if fleas were excluded young 

 rats could suckle a plague-infected mother without contracting the 

 disease, 



