SarcoptideB Psorica. 157 



male perishes, and the female passes through another moulting 

 and becomes the ovigerous female. 



4. The Ovigerous Female. This shows a sub-thoracic vulva, 

 one or more eggs seen through its usually transparent body, and 

 changes in the third or fourth pair of legs, or both. 



Fecundity. Encrease. The fecundity is remarkable. 

 Gudden found 51 empty egg shells in a single sarcoptes gallery, 

 and Walz, Hertwig and Gerlach determined that a new genera- 

 tion of sarcoptes hominis succeeded the old and gained maturity 

 in 15 days. Placing the egg product of a single female at 15, 

 Gerlach estimated the natural encrease to be 1,500,000 in ninety 

 days. Noticing that a few seconds contact of a sound horse with 

 a mangy one caused in about 10 or 12 days the development of 

 myriads of acari on the former, Megnin estimates the encrease of 

 the sarcoptes of the horse as follows : 



1st generation after 10 days 



2d 



3d 



4th 



5th 



6th 



20 

 30 

 40 

 50 

 60 



Vitality. Gerlach made some interesting experiments to deter- 

 mine the vital tenacity of psoric acari. He found that all the sar- 

 coptes died in an hour in a dry heat of 145° Fah. The sarcoptes 

 equi died in 5 to 6 days when placed with its crusts in a show 

 glass, or from 12 to 14 days if placed in an inhabited stable. On 

 a piece of skin covered with crusts and exposed to a very moder- 

 ate temperature, they died in 9 days, on the drying of the skin ; 

 but if the skin were kept humid the acarus showed signs of life on 

 the 24th day but none on the 28th. The psoroptes equi lived 10 

 to 14 days in a dry atmosphere and 20 to 30 in a stable. Though 

 torpid and apparently dead, the acarus, revived after 6 or 8 weeks 

 when subjected to moist warmth. The symbiotes lived in their 

 cru.sts in a dry warm room for 10 to 12 days, and though after 

 this they were apparently dead, they revived after 14 days under 

 the influence of moist warmth. In spring, in a non-heated 

 chamber they lived 40 days and in a stable not less than 50. 



Divisions and Habits of Psoric Acari. The acari which 

 cause the common forms of scabies are naturally divided into the 



