﻿THE CATTLE GRUBS OR. OX WARBLES 39 



In the case of the cow infested at the base of the ear (No. 25-D) 

 the first larva reached the back October IT. 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 larvse taken from 

 the gullet of a slaughtered animal. These larvae 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 larvse 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 larvse 

 by placing them on tlie 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 larvse through the 

 mouth. In all of these animals larvse 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. Iv-23), which received eggs on the back, developed 

 nine lar^-se in that region. The date of first appearance of larvse 

 in the subdermal tissue was not influenced materially by the elate 

 of infestation or by the point of ingress into the animal. 



On November 14, 1923, 20 larvse 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 

 sbout 6 inches above the hock joint on the outside of the right hind 

 leg. The larvse averaged slightly over 12 millimeters in length. 

 On November 19 the older calf (No. 92-1) (1 month old) was dis- 

 sected and 15 larvae 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 

 larvse 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 

 larvse from gullets were put under the skin of this calf on the left 

 hind leg just above the hock. These wei'e from 12 to 16 millimeters 

 in length. Immediately ])re -edinor Januarv 8. 12 grubs had reached 

 the Jjafk and had pnnctiired the skin. These Avere about equally 

 (listiHtnted on each side of the spine; 7 others reached the back by 

 Januai-y 22, making a total of 25. On Defcmber 28. 29 lai'vie from 

 12 to 16 millimeters in length weie introdufcd in an incision through 

 the skin on the right hind leg of a cow, just above the hock. On 

 January 7, or shortly beffjre. the first larva appeared behind the 

 right hip, and 7 others cut holes through the skin during the period 

 up to Janiuii-y 18. One of these was only 7 inch<'s above the point 

 of introduction and the last one was on (he h'f( side just in front 

 of the hi|;. a distance of about 33 inches from Ihc point of intro- 

 duction. 



