GERLACH ON THE ITCH AND MANGE. 163 



so that the skin does not bear so distinct an indication of 

 being affected where the male acari exist, as where the 

 femal' s are lodged, in deep furrows, giving rise to much irri- 

 tation. 



Eeferring to the incubation of the eggs of sarcoptes 

 hominis, the author avers that all the statements hitherto 

 made are incorrect, not excluding Bourguignon's. The 

 changes which the latter gentleman declares to have observed 

 in the course of ten days, occur, according to Gerlach, in the 

 incredibly short period of three days. A very simple process 

 was adopted by Gerlach to prove this. He placed some eggs 

 of sarcoptes hominis in a depression on a piece of glass plate, 

 and having added a few drops of water, another bit of glass 

 was gummed over the cell containing the eggs, and the 

 apparatus was then bound round the arm; every twelve 

 hours a few drops of water or saliva were added. Some- 

 times the incubating apparatus was carried about in a 

 pocket close to the body, and generally the eggs were 

 hatched in three days, and not usually in more than three 

 days and a few hours. This explains the rapidity with 

 which a person may be covered with acari, though only one 

 or two might have crawled on the body at first. 



It is probable that so soon as the female has deposited her 

 eggs she dies, and Gerlach believes that her life does not ex- 

 tend to more than four or five weeks. The males do not die 

 after sexual intercourse, and one male may fecundate many 

 females, a proof of the necessity for less males than females. 



When removed from the skin, sarcoptes die more from 

 drying and shrivelling up than from hunger. Under the in- 

 fluence of dry heat they soon become weak, and perish in 

 from three to four days. If they are kept in a warm and 

 moist medium, they may survive eight or ten days. 



We need not dilate here on the characters of the itch 



