81 



Weekly disiufectiou is found to he necessary at first, but once 

 the birds are healthy and the runs and houses clean, the interval 

 may be considerably increased. The frequency of the application 

 should, to some extent, be determined by the climate and the 

 season of the year. A knapsack sprayer or a garden sj^ringe 

 serve the purpose better than a watering-can. 



Stockmax (Sir S.) & Beury (A. H.). The Psoioptes commvuis 

 oris; some observations on Ova and Ovipositing.— ./Z. Comp. 

 Fatli. cj- Therap., xxvi, pt. 1, Marcli 191:), pp. 45-50. 



This article is the continuation of ^vork previously recorded in 

 the annual report of the Chief Veterinary Ofiicer, Board of Agri- 

 culture and Fisheries, 1911, and Jl. Comp. Path, and Therap., 

 1910. One of the chief points investigated was the number of 

 eggs laid by each female, the authors having found that the 

 female is usually oviparous, though on two occasions specimens 

 were found which contained eggs including apparently fully 

 developed larvae. If females are taken from a sheep, placed 

 in a glass dish or tube and incubated, a considerable proportion 

 of them will lay, but it was found to be exceptional for the female 

 to lay more than one egg after being removed from its host, unless 

 it were returned to the sheep for further feeding. On only one 

 occasion did the specimen lay two eggs. The ova require an 

 average of 100 liours for liatching, in a slightly moist atmosphere. 

 Some do not hatch until the sixth or even the seventh day. AVhile 

 the authors confirm the observation of Cerlach that the average 

 number of eggs laid is about fifteen, they are nevertheless of 

 opinion, as the result of numerous observations, that this number 

 may be considerably exceeded, in some cases rising to even more 

 than thirty. The process of oviposition is slow; two eggs in 

 twenty hours, or three in twenty-four, seems to be about the 

 average rate, and the Avliole period of oviposition lasted about 

 eight days, after which the females appeared to die. The period 

 required by the acarus to pass through all its stages is about 

 twelve days. In some cases the females, for some unknown 

 reason, decline to produce eggs for a considerable time after being- 

 put on the sheep. The authors are of opinion that an outbreak 

 of sheep scab may be started by one fecundated ovigerous female, 

 and they also think that their observations provide a further 

 explanation of the long intervals which frequently elapse in 

 practice between contact with infection and the appearance of 

 the visible scab. 



Observations have shown that living larvae are seldom found 

 on sheep after dipping, and they were subsequently able to show 

 that after dipping scabby sheep in arsenical dips a few larvae 

 may hatch out, but that these usually leave the dipped sheep. 

 This was found not to be the case with dips of the creosote type, 

 and it was therefore considered advisable to make experiments 

 in vitro, with the following results : — 



Two lots of eggs, numbering 60 and 30 respectively, were 

 immersed in an arsenical dip for one minute and then incubated; 



