PREVENTIVE MEDICINE 351 



The larvae may become attached to the mucous membrane of the 

 pharynx, and Canon has recorded the presence of G. pecorum in the 

 pharynx of 15 horses that came from South Africa.* Bots may 

 set up pharyngitis and sometimes, though rarely, gastritis. The 

 stomach seems capable of carrying enormous numbers of these 

 parasites without any obvious harm or malaise accruing, but per- 

 foration of the gastric wall sometimes results with a fatal ending. 



PREVENTION of infestation may be at least partially secured 

 by smearing the legs of horses during the fly season with an oily 

 dressing containing tar or creosote, or with common paraffin oil. 

 General Sir Frederick Smith has recommended a weekly singeing 

 of the egg area of horses at grass. 



LICE. 



Lice are readily divided into two distinct classes (a) the Blood- 

 Sucking Lice, which include the Pediculince of man and Hcemat- 

 opinidce of animals, and (b) the Scurf or Feather-Eating Lice 

 which include the Trichodcctida and Gryopida of animals and the 

 Menopenida of birds. 



Lice of both classes are found on all domestic animals. Those 

 of the first class are the more injurious, as not only do they cause, 

 as a rule, greater irritation and quite an appreciable loss of blood, 

 but they are in many cases disease carriers e.g., in the human 

 subject the great scourges of war, typhus and trench fever, are 

 carried by Pediculida. A few of the second class also carry patho- 

 genic parasites e.g., the Trichodect of the dog is known to carry 

 the larval stage of Dipylidium caninum. 



While the presence of lice is, in general, indicative of neglect 

 and dirt, it must be remembered that some animals are peculiarly 

 attractive to these vermin. Old age and an impoverished condition 

 of the body undoubtedly predispose to lice infestation. 



The life-cycle of the louse is comparatively a simple one. The 

 female lays about a hundred eggs and each one is attached singly 

 by a glutenous material to the base of a hair. The eggs or " nits " 

 hatch into young lice in from fourteen days to a month, and these 

 after feeding and moulting become adult. 



Warburtanf found that with human lice the eggs hatched in 

 from 8 days to 5 weeks; the larval stage lasted 11 days; a male 

 lived 3 weeks and a female 4 weeks. He considers that under 



* Vet. Record, XXX., p. 107. 

 t Quoted by Macdougall, Trans. High Agric. Soc., 1916, XXVIII., p. 108. 



