24 INSECTS AFFECTING DOMESTIC ANIMALS. 
in a separate chapter, and we wish here only to allude in the briefest 
manner to a few general principles which should be kept in mind in all 
cases of insect attack upon domestic animals. 
As with many other insects, it is frequently much easier to prevent 
than to remedy, and if careful attention is given to the matter the 
stock breeder may, for many of the pests here enumerated, gain for his 
herds practical immunity, even if other herds in the vicinity are 
infested. This is true for all species that are incapable of flight, or that 
depend for distribution on the direct association of infested animals 
with those that are free, or that, by attaching themselves to posts, rails, 
etc., where animals rub themselves, may be transferred from one to 
another. Prevention is also the most important measure with the 
internal parasites, bots, ete., which are with difficulty reached when 
lodged. With many others, however, such as mosquitoes, flies, ticks, 
etc., and with lice, mites, etc., if they have gained a foothold, direct 
treatment is absolutely essential. Here there is necessity for examina- 
tion of the conditions and adoption of one of two forms of treatment, 
according to the circumstances. The first, repellant, where, as with 
mosquitoes, flies, ete., it is possible to drive the insects from any par- 
ticular animal by mechanical devices or by use of repelling odors. The 
secon 1, destructive, where it is necessary by use of substances fatal to 
the parasite to cause its death. In all of these there is choice among a 
number of fairly successful measures, each of which may have some 
particular advantage under certain circumstances. For example, dips 
and washes, which may be safe enough in hot weather, may be unde- 
sirable in winter. On this account it has seemed that some method of 
fumigation might prove of value, and experiments in this line have been 
made which show that it can be used effectively. The time required, 
however, to do this makes other methods still preferable. Doubtless 
some improvements in details of application may much facilitate treat- 
ment in this manner, and we would call attention to te subject dis- 
cussed more fully in Chapter VEE 
