42 BULLETIN 597, U. S. DEPARTMENT OF AGRICULTURE. 
The @. intestinalis are the most resistant of the Gastrophilus to 
treatments, but these, being found in the stomach, are in the most fa- 
vorable place for treatment. No immediate effects of the gas upon last- 
stage Gastrophilus larvee are observed, as they remain motionless for 
some time. Finally they contract so as to conceal the hooks of attach- 
ment and then drop from the stomach section. This sometimes occurs 
within 30 minutes after the fumigation begins, but most often it is 
after 1 or 2 hours. Occasionally the contraction is not so great and 
larve remain attached but drop at the slightest touch. A number of 
observations were made upon animals treated by local veterinarians. 
During the spring and early summer records were kept on 23 of these 
horses, which were treated when they contained only last-stage larvee. 
The treatment was given as recommended by the Bureau of Animal 
Industry. Within 36 to 48 hours the first bots appear in the feces, 
though if the physic acts well they may be found after 24 hours. The 
writer observed bots to pass for a period of 5 days, beginning about 
36 hours after the treatment. With the first droppings a few living 
larve may be found which detached from the stomach before the 
treatment, and in one case G. nasalis was reared from such larve. 
G. haemorrhoidalis may appear at the anus as usual if this treat- 
ment is given in the spring, as by this time numbers have previously 
migrated to the rectum. | 
While Table IX shows that carbon disulphid gas is capable of 
killing last-stage larvee within 34 hours, the ideal time for treatment 
of horses would be in the autumn when all larve are young and the 
G. haemorrhoidalis are still within the stomach and duodenum. The 
last-mentioned experiments in Table IX show some fumigation re- 
sults with small Gastrophilus. It will be observed that 1 hour was 
an amply sufficient time, though a few last-stage larvee were present 
as late as September 18. If not caused to detach these would possibly 
drop during the winter and succumb to low temperatures. In Dallas, 
Tex., 45 minutes was sufficient to kill young larve on December 9, 
1916. 
The fact that G. nasalis attaches in the throat, where the larve are 
not in a position to be affected by the carbon disulphid treatment, em- 
- phasizes the fact that “an ounce of prevention is worth a pound of 
cure.” 
REPELLENTS. 
The rubbing of horses upon posts, bowlders, and other convenient 
objects suggested a device for use in pasture whereby horses could 
rub their lips upon a repellent. The short period of effectiveness of 
repellent substances and the inability to obtain one that will remain 
on the lips during grazing are difficulties which would seem to be 
overcome by such a device. A keg reservoir was devised whereby a 
