392 Haematopinus asini 
This, if correct, would mean that supposing all active stages are killed at 
each dressing and the treatment repeated at ten-day intervals, four dressings 
at least must be given, for, although no more eggs will be laid during the period 
over which the dressings extend, there is every probability that if this period 
is curtailed a few of the original stock may hatch after a month and restart 
the infestation. 
2. The normal incubation period would appear to be 16-20 days, and the 
minimum period, under natural conditions, about 15-16 days. 
3. A very small amount of dry heat will kill eggs. Even at blood heat it 
was found that 24 hours in a dry atmosphere prevented hatching. 
It is evidently due to the effect of temperature that the lice in hot weather 
migrate to sheltered parts of the body. The eggs are usually laid close to the 
skin, and, in a partly clipped horse, the lice migrate to the unclipped portions. 
4. Moist cold kills the eggs, whereas dry cold only has the effect of length¬ 
ening the incubation period by a few days. How long they can withstand this 
dry cold has not yet been determined, but a week in a cold dry room with 
a temperature of about 50° F. resulted in killing about 50 per cent, and 
lengthening the incubation period of the remainder from the normal 16 days 
at 100° F. to 18 days. 
ERRATUM TO VOL. XI. 
p. 225, line 12, read 0-5 (caustic soda 0*5 pt.) for 5 
