46 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTURE 
for periods of from 10 to 30 minutes, but they were not allowed 
to remain indefinitely. Aithough some of the larve made slight 
attempts to penetrate into hair follicles, in no case did they 
succeed in making much progress. In one instance a number of 
larvee were placed on the conjunctiva of the eye of a rabbit. Thev 
moved about actively for some time and could be seen for an hour 
or more in the conjunctival region, but apparently they made no 
von to penetrate, and produced only a very slight irritation to 
the eye. 
The writers have made no observations on the penetration of larve 
of 17. bovis, but have frequently observed the lesions produced by the 
burrowing of this species. | 
In 1914 (77) Carpenter, Hewitt, and Reddin recorded observations 
on the penetration of H/. lineatwm through the skin of cattle at 
points where eggs were attached. In addition to finding lesions at 
those points they succeeded in squeezing from the penetration holes 
along with serum a newly hatched maggot of this species. In the 
same publication the authors record observations on the penetration 
of first-stage larve of H. bovis, stating that it required about six 
hours for them to get into the skin. Prior to this Glaser (29) had 
failed in attempts to get the young larve to penetrate through the 
shaven skin, but in one case previously mentioned the larve pene- 
trated through the skin on his own leg. The time occupied from the 
detection of the presence of the larva until it had disappeared was 
one and three-fourths hours. 
In 1916 (53) Hadwen published a number of observations on the 
action of larve, both on living hosts and on pieces of skin freshly 
cut from cattle. He failed to observe the penetration of larve on 
living animals, but in a number of tests on hide removed from a 
bovine he observed larvee to burrow partially, and in a few cases 
completely out of sight. 
LESIONS PRODUCED BY THE PENETRATION OF FIRST-STAGE LARVZ 
The presence of exudate and pimples on cattle immediately under 
the eggs of Hypoderma from which the larve had emerged was 
first recorded by Carpenter, Hewitt, and Reddin in 1914 (17). 
Hadwen (33) has rather fully described the skin lesions of the 
two species of Hypoderma. He proposes the name “ hypodermal 
rash” for the condition resulting from larval penetration. 
When the newly hatched larvee have burrowed into the skin and 
when their posterior segments are about flush with the skin sur- 
face there begins to appear a watery secretion, presumably blood 
serum. After the larva disappears this exudate increases in quan- 
tity and several hours later small pimples form which in some 
instances, at least, have been found to contain pus. In the case 
of H. lineatum where a number of larve often penetrate near one 
another, the inflammation and exudate become more marked and 
often the hair is matted, making a scab. . With lZineatum this irrita- 
tion is often very marked, the entire area near where the penetra- 
tion occurs becomes swollen, and in certain instances where a large 
number of larve have penetrated the heels of a calf the hind leg 
from the hock down has been observed to be swollen. These swol- 
Jen areas are more apparent when large numbers of eggs are de- 
