356 VETERINARY HYGIENE 



measure, but unfortunately much tick- infested land is quite unsuit- 

 able for the plough. Periodic dipping of cattle and sheep, prefer- 

 ably with arsenical dips, or spraying with paraffin emulsion are 

 recommended. Sheep may be grazed on land infested with red- 

 water-carrying ticks ; this serves to collect the ticks, which may then 

 be destroyed by dipping. 



PARASITIC MANGE. 



General Statement. The mange mites are epidermal parasites 

 which, though the various genera differ in some important points 

 in their mode of life on their hosts, all possess certain similar 

 features that are of considerable importance to the hygienist. 

 Those that call for attention are : Sar copies, Notoedres, Cnemido- 

 coptes, Psoroptes, and Symbiotes or Chorioptes. 



The mites are, in general, oviparous, and it takes about four 

 weeks for the life-cycle to be completed. Roughly, the sequence 

 is as follows : a hexapod larva develops from the fertilised egg 

 in from 4 to 7 days, which by moulting becomes in 3 or 4 days an 

 octopod but sexless nymph. By a further 3 or 4 days the nymph 

 has become adult. Oviposition takes place about a week after 

 copulation. Gerlach* estimated that one generation, about one and 

 a half million progeny, should develop in the course of three months. 

 It is said that eggs fail to develop away from the warmth and 

 moisture of the body. 



Resistance of Mange Mites. According to Hertwigf mange 

 mites die in a few days if placed exposed in a room, probably on 

 account of the lack of moisture. If kept moist on the skin they may 

 live for three weeks or more, but in a dry atmosphere they die in 

 fourteen days. Brandl and Gmeimer conclude that the optimum 

 temperature for mange mites is from 59 to 86 F., and that at 

 97 F. they become dry and shrivel. In warm water, according to 

 these investigators, the mites live for twelve to fourteen days, 

 and in cold water for nine to twelve days. Testing the action of 

 certain chemicals on the mites, the above workers found that 

 chloroform, bisulphide of carbon, and glacial acetic acid immedi- 

 ately kill them. Liquor cresoli saponis and carbolic acid in 2 

 per cent, watery solution kill in from two to three minutes. A 1 

 per cent bichloride solution takes half an hour and a 20 per cent, 

 decoction of tobacco leaves did not destroy the mites in three hours. 



* Epizootics and their Control during the War, Miessner, 1915, English 

 Trans, by Liebold, 1917, Vet. Med. Series, No. 15, Chicago, 

 f Epizootics and their Control. 



