MANGE. 



549 



been excellent guides for investigators. Among recent literature 

 we must particularly mention that of Robin, Mégnin, and Zurn. 



Morphology and biology of psoroptic Acaei. The specific 

 agents of mange constitute a group of the Arthropodes, of the class 

 Arachnides, the order Acari, and the family Sarcoptes. Their 

 dimensions vary between 0.2 and 0.8 millimetre; their general 

 form is rounded or ovoid ; in their immature form they have three 

 pairs of legs, in the adult state they possess four ; the latter, with 

 five joints, are fitted with mcurhitula (suction cups), covered with 

 fine hair, and armed with claws (hooks); the head, thorax, and 

 abdomen are not separated ; the organs of mastication are repre- 

 sented by mandibles ; the cutaneous surface is covered with scales, 

 hair, spikes, or silky hair, etc. The females, which are larger than 

 the males, lay from twenty to twenty-four eggs ; at the end of four 

 to seven days the larvse come out, and after having undergone three 

 to four metamorphoses, arrive at the stage of reproduction from the 

 fourteenth to the seventeenth day. Concerning the psoroptes of 

 the sheep, Gerlach has calculated that one female alone may pro- 

 duce 1,500,000 individuals in ninety days. The females die in 

 from three to five weeks after laying ; the males live about six 

 weeks. If exposed to damp air or placed upon wet manure the 

 acari continue to live from six to eight weeks ; in dry air they die 

 within two to three weeks ; upon damp ground the eggs remain 

 alive for from two to four weeks ; in a dry place they lose their 

 vitality after four to six days. A moderate heat is favorable to 

 their vitality and to the pullulation of the parasites ; in warm 

 places, under cover, and during the summer their movements are 

 more active and they multiply more rapidly than under the oppo- 

 site conditions. According to Gerlach, the medicines which kill 

 these parasites most rapidly are: creosote (fifteen to thirty seconds), 

 caustic potash in a solution of 1 : 25 (two minutes), essence of tur- 

 pentine (five to ten minutes), petroleum (seven minutes), tar (eight 

 to thirteen minutes), tobacco (1 part to 5 of water, ten to twenty 

 minutes ; 1 part to ten, two to five hours ; 1 part to 50, four to ten 

 hours), liver of sulphur at 1 : 10 (in a quarter to half an hour), 

 green soap (half an hour to one hour, etc.). (For further details on 

 the biology of acari, see treatises on general pathology and para- 

 sitology.) 



Kinds and specieSc We must examine the various kinds suc- 

 cessively : 



