| THE CATTLE GRUBS OR OX WARBLES gf: 39 
In the case of the cow infested at the base of the ear (No. 25-D) 
the first larva reached the back October 17, and a total of 15 came 
to that region; with the cow infested on the back (No. 167) only 
two appeared (November 8 to 12). On November 16 a bull calf was 
infested in the hind leg by inserting in the skin 14 larve taken from 
the gullet of a slaughtered animal. These larve measured 11 to 
15 millimeters in length and the first appeared on the back November 
30. Nine of the 14 succeeded in coming to the back for normal 
development. 
In the calf (No. 24-D) five first-stage larvee were applied for a 
study of penetration. Although some of these were observed to 
penetrate the skin, none reached the back. 
During 1922 seven cattle were used in the tests. One of these 
(No. 92) was protected from flies, but fed 89 newly hatched larve 
by placing them on the tongue and in the lips. In this animal not 
a single larva reached the back the following fall and winter. Of 
the other six hosts, five were infested on the heels and legs and 
muzzled to prevent ingress of newly hatched larve through the 
mouth. In all of these animals larve reached the back, the number 
per host varying from 1 to 26, despite the fact that two of the ani- 
mals had the legs immersed in insecticides every day. The other 
animal (No. K-23), which received eggs on the back, developed 
nine larve in that region. The date of first appearance of larve 
in the subdermal tissue was not influenced materially by the date 
of infestation or by the point of ingress into the animal. 
On November 14, 1923, 20 larve taken from the gullets of slaugh- 
tered cattle were placed beneath the skin by incision, on each of two 
calves (Nos. 92-1 and 25D-1). The point of introduction was 
about 6 inches above the hock joint on the outside of the right hind 
leg. The larve averaged slightly over 12 millimeters in length. 
On November 19 the older calf (No. 92-1) (1 month old) was dis- 
sected and 15 larvee were recovered. Most of these were ranging 
upward in the connective tissue under the skin where there was 
marked infiltration, and one had passed between muscles on the rear 
of the thigh and was apparently following a large nerve, being only 
3 inches from the spinal canal. In the other calf (No. 25D-1) 6 
larve had reached the back and had perforated the skin, 4 on the 
right and 2 on the left side. On December 28 another lot of 16 
larvee from gullets were put under the skin of this calf on the left 
hind leg just above the hock. These were from 12 to 16 millimeters 
in length. Immediately preceding January 8. 12 grubs had reached 
the back and had punctured the skin. These were about equally 
distributed on each side of the spine; 7 others reached the back by 
January 22, making a total of 25. On December 28, 29 larvee from 
12 to 16 millimeters in length were introduced in an incision through 
the skin on the right hind lee of a cow, just above the hock. On 
January 7, or shortly before, the first larva appeared behind the 
right hip, and 7 others cut holes through the skin during the period 
up to January 18. One of these was only 7 inches above the point 
of introduction and the last one was on the left side just in front 
et oe hip, a distance of about 33 inches from the point of intro- 
uction, 
