104 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
of cattle by the application of insecticides. The difficulty of re- § 
moving the grubs from certain breeds, however, led them to give © 
very serious consideration to this method of treatment. As a re-— 
sult of rather extended experiments and practical demonstrations 
of this method, it became evident that no ill effects were visible © 
in the host. It is true that certain materials may be used in the 
destruction of the grubs which are detrimental to the host, as, for — 
instance, copper sulfate. In the writers’ tests this material gave — 
decidedly bad local effects. Abscesses were developed in a con- | 
siderable percentage of the cysts treated. On the other hand, with 
many of the most effective larvicides tried, pus formation in the © 
cysts was checked and the size of the lump caused by the grub was 
rapidly reduced. 
With some treatments, notably those with carbon tetrachloride, 
and with derris in various forms, the exit holes of the grubs were 
observed to close rather rapidly and there was little tendency for 
the host to expel the insect. In most instances the grubs were found 
to disintegrate rather rapidly under such conditions, especially if — 
they were not in the late stages of development. At times some of 
the grubs, especially in the late fifth stage, were found to rise in 
the aperture in the skin and the posterior segments to harden, thus 
retarding the closing of the hole in the skin. | 
When the grubs are not further developed than the early part of | 
the fifth stage, they are promptly absorbed after being killed by 
substances apphed to the back of the host. After the skin and 
spines have become thoroughly chitinized their elimination by the 
host is more difficult. Some collapse and work out or are licked 
out of the skin. Most of them are reduced in bulk by absorption — 
and the skin heals up smoothly over them. A considerable per- 
centage of these mature grubs may remain in the skin for several 
months. This shows the advisability of applying treatments while 
the grubs are young; furthermore, at this time the holes in the 
hides are much smaller and heal up more quickly. 
When ointments such as iodoform, derris, or pyrethrum and 
petrolatum are used, the writers have found that a considerable 
percentage of the grubs are expelled from the cysts after their — 
death. Some of them are found completely emerged from the skin ~ 
of the host two days after treatment and they continue to be thrown 
off for about two weeks. Some project slightly from the skin and — 
may remain so for weeks if not mechanically removed. The per- | 
centage of grubs which are expelled after treatment varies widely, 
apparently differing with the character of the skin of the host. | 
In order to determine the effect on the host and the rapidity — 
of healing of the grub holes, some special observations were made — 
on herds (1) where grubs left the hosts normally, (2) where the 
larve were punctured and pulled out, (3) where they were ex- 
tracted by hand, and (4) where various materials were applied 
to the backs of the cattle. The rapidity of healing of the grub 
holes was found to vary much in different animals, both when the 
grubs emerged normally and when they were extracted or destroyed — 
in situ. It was found that the time required for healing of holes 
where the grubs emerged normally ranged from about 13 to 76 — 
days. The scars from the skin injury often persist for several 
months. The presence of foreign material in the form of a plug in 
