6o2 



Plague 



of desertion, occupied by a welcoming host of fleas. They are the progeny of the 

 fleas of the former dog, cat, rat or mouse tenants, that have matured or survived 

 the interval and are now hungry because the removal of the family months before, 

 was probably followed by the withdrawal of the rats and mice no longer able to 

 find food in the deserted habitation. 



To get rid of such fleas is often a perplexing question. A way to accomplish 

 it is to place a cage containing a cat or a guinea-pig, or a trap containing living rats 

 or mice on the floor of a room and surround it by sticky fly-paper. Fleas when 

 empty and hungry, were found by Strickland* to be able to jump 4 inches; 

 those recently fed only 3 inches. In their endeavors to reach the caged animals 

 the fleas jump upon the fly-paper and are caught. This can be done in several 

 rooms of the house and soon cleans up the fleas. 



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Fig. 240. — Various fleas, magnified about 30 diameters. The specimens are 

 treated with hot 20 per cent, caustic potash for a few minutes, dehydrated in 

 alcohol, cleared in xylol and mounted in balsam, a, Pulex irritans, & ; b, Pulex 

 irritans, 9 ; c, Xenopsylla cheopis,d'; d, Xenopsylla cheopis, 9 (Bacot, in Jour- 

 nal of Hygiene, "Plague Supplement ni, 1914"). 



During such periods of fasting the sexes do not copulate and no ova are pro 

 duced. As soon as blood is taken, copulation takes place; and if the blood be 

 that of the preferred host, ovulation follows in about twenty-four hours. The 

 eggs are relatively large, and small numbers are produced. 



In the case of Sarcopsylla penetrans, a flea that has no known interest in con- 

 nection with plague transmission, the female after copulation imbeds itself in the 

 skin of the host and sufifers an enormous saccular distension of the abdomen where 

 many ova are produced. Ordinary fleas never imbed themselves but simply bite 

 and suck blood, leaping off the host when satisfied. 



Epidemics of plague among men are commonly preceded by epizootics of plague 

 among rats. The mortality of the rats being high and their number diminishing, 

 many fleas are unprovided for and seek human hosts upon whom to satisfy their 

 appetites. In this way, the plague which was at first transmitted by the fleas to 



'Journal of Hygiene," 1914, xiv, p. lag. 



