vi INSECTA 255 



stand water. In order to get rid of larvae already existing some dis- 

 infectant such as cresol should be added to the water (i in 20). 



Of the ordinary fleas those of the Rat (especially Pulex, or Xenopsylla, 

 cheopis the common rat-flea of the tropics) are of special importance, 

 for plague is normally a disease of rats, and fleas feeding on infected 

 individuals become themselves infective and capable of inoculating 

 human beings by their bite. Fleas, in fact, are the regular means by 

 which plague is spread both from rat to man, and from one human being 

 to another. 



A peculiarly modified flea which gives trouble in dry tropical regions 

 is the jigger or chigoe (Sarcopsylla penetrans). In this case the fertilized 

 female burrows into the skin, preferably of the toe, until completely 

 hidden except the tip of the abdomen. The abdomen eventually becomes 

 greatly distended reaching the size of a small pea. The eggs are shed 

 to the exterior, and if the stockings are not frequently changed the larvae 

 may undergo their complete development therein and the feet become 

 infested by a large number of jiggers. The jigger under normal circum- 

 stances does not cause pain, the sensation being a mere slight itching 

 feeling, but there is always a chance of sepsis being set up by some 

 microbe getting into the wound. Consequently care should be taken 

 when extracting the jigger to use iodine or some other efficient antiseptic. 



Jiggers are common in the warmer parts of the New World, infesting 

 the feet of human beings and also of dogs. Introduced into West Africa 

 they have spread across the continent, and will no doubt in time establish 

 themselves in all tropical countries. 



The Lice (ANOPLURA) are small soft-skinned insects which live on the 

 skin of mammals. Two species (i) Pediculus humanus, with its two 

 varieties the Head Louse (" P. capitis ") and the Body Louse (" P. 

 vestimenti "), and (2) the Crab Louse (Phthirius pubis) are common 

 parasites of man where uncleanly conditions prevail. Any one whose 

 occupation takes him into proximity to uncleanly persons is liable to be 

 attacked by these pests and these attacks are now known to be not 

 merely unpleasant but dangerous, as it has been clearly shown that lice 

 are responsible for the spread of Typhus, " European " Relapsing Fever 

 and Trench Fever. The infection is as a rule not conveyed by the microbe 

 being injected with the salivary secretion. The microbes gain access to 

 the body through abrasions caused by scratching or other breaks in the 

 skin. And in the case of trench fever dried excreta from the insect, 

 such as may readily be blown about as dust, are capable of causing 

 infection if they get into wounds of the skin. 



The MALLOPHAGA or Biting Lice include a large number of parasites 



