166 



APPLIED ENTOMOLOGY 



Rather recently it has been discovered that the hce of man are con- 

 cerned in the transmission of Relapsing fever, Trench fever, and that 

 terrible disease Typhus fever. It does not at present seem that the 

 causal agents of the first two of these are actually transferred to man 

 by the feeding of the infested lice, but rather that these agents are present 

 in their bodies and feces, and that by scratching parts irritated, fluids from 

 crushed lice or the feces get rubbed into the irritated areas, are able to 

 enter the body, reach the blood and begin the disease. This also 

 appears to be true in the case of Typhus fever, but here inoculation by the 

 feeding of the lice also seems probable. In some cases where scratching 

 does not occur but where Relapsing or Trench fever nevertheless develops, 

 it is probable that the feces get into the feeding wounds and in that way 

 cause the disease. 



The Crab Louse {Phthirus pubis L.). — This louse is quite different 

 in appearance from the last, being smaller, shorter, broader, and with 



its legs projecting outwardly near together 

 (Fig. 158). The fore legs are slender but 

 the others are stout and each has a powerful 

 serrated claw which shuts against a pro- 

 jection of the preceding segment of the leg 

 in such a way as to give a very firm grip 

 on a hair. This insect is found primarily 

 on the hairy parts of the body except the 

 head, but in exceptional cases it may be 

 found there also. It holds onto the hairs 

 while feeding and in moving about always 

 holds tightly to hairs on one side until it 

 has obtained a grasp on others on the 

 other side. This gives it a sideways move- 

 ment which is responsible for its common name. Its life history is 

 much the same as in the other species. 



Washing thoroughly with tincture of larkspur as for the head louse 

 is usually an effective treatment. An ointment made of 4 parts of crude 

 naphthaline mixed with 1 part of soft soap rubbed on the undercloth- 

 ing in the infested region has also been found to be a very successful 

 treatment. 



Lice on Domestic Animals. — These are sometimes serious in their 

 attacks, weakening the animal greatly if they are abundant. In the 

 treatment of these pests it should be borne in mind that poisonous 

 materials cannot be used because of the danger coming from the animals' 

 licking themselves. Various substances have been used for hve stock, 

 such as 15 per cent kerosene emulsion scrubbed on the skin; washing 

 with potassium sulfid, using from 2 to 4 oz. per gallon of water according 

 to the size and vigor of the animal; the application of a mixture of sulfur 



Fig. 158. — Human Crab Louse 

 (Phthirus pubis L.) about twelve 

 times natural size. (From Berlese.) 



