﻿46 BULLETIN 1369, U. S. DEPAETMEKTT OF AGEICULTUKE 



for periods of from 10 to 30 minutes, but they were not allowed 

 to remain indefinitely. Although some of the larvae made slight 

 attempts to penetrate into hair follicles, in no case did they 

 succeed in making much progress. In one instance a number of 

 larvse were placed on the conjunctiva of the eye of a rabbit. They 

 moved about actively for some time and could be seen for an hour 

 or more in the conjunctival region, but apparently they made no 

 effort to penetrate, and produced only a very slight irritation to 

 the eye. 



The writers have made no observations on the penetration of larvae 

 of H. hovis^ 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. Ihieatum 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 larva? of H. hovis^ 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 larva? to penetrate through the 

 shaven skin, but in one case previously mentioned the larvae pene- 

 trated through the sldn 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 (33) Hadwen published a number of observations on the 

 action of larvae, both on living hosts and on pieces of skin freshly 

 cut from cattle. He failed to observe the penetration of larvae on 

 living animals, but in a number of tests on hide removed from a 

 bovine he obserA-ed larvae to burrow partially, and in a few cases 

 completely out of sight. 



LESIONS PRODUCED BY THE PENETRATION OF FIRST-STAGE LARV^ 



The presence of exudate and pimples on cattle immediately under 

 the eggs of Hypoderma from which the larvae 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 larvae 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. lineatwm where a number of larvae often penetrate near one 

 another, the inflammation and exudate become more marked and 

 often the hair is matted, making a scab. With lineatum 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 larvae have penetrated the heels of a calf the hind leg 

 from the hock down has been observed to be swollen. These swol- 

 len areas are more apparent when large numbers of eggs are de- 



