﻿4 BULLETIN 1369, U. S. DEPARTMENT OF AGRICULTUEE 



in Holland, gave definite proof that the small larvse found in the 

 spinal column of cattle were really Hypoderma. Some of these were 

 introduced under the skin of a goat, and 12 days afterwards swellings 

 appeared, from which later H. hovis was reared. In the same article . 

 he also described experiments in which 26 larvse from the spinal 

 canal of cattle were introduced under the' skin of a dog. When the 

 animal was examined two weeks later some of the larvse were found 

 in various parts of the animal, including the gullet and spinal canal. 

 Similar larvse fed to dogs and introduced into the gullet of a rabbit 

 through a tube were not recovered. From these tests Koorevaar 

 concludes that in bovines the larvse reach the gullet or spinal canal 

 after extensive wanderings from the place where they bored through 

 the skin, and that they do not reach the gullet by way of the mouth. 

 Further studies on the migration and seasonal occurrence of the larvse 

 within the host were published the same year by Koorevaar {55). 



FoUoT^'ing the publication by Curtice and the subsequent one by 

 Eiley, practically all scientists accepted Curtice's theory. In 1903 

 Koch {53) published a very valuable contribution as the result of 

 several years' study of the larvse of Hypoderma within the bodies 

 of cattle. He shows that the young larvse are widely distributed 

 within the body cavity and in the intermuscular tissues of the back, 

 and that larvse as small as 2.2 millimeters in length may be found 

 in the submucous tissues of the gullet. He concludes from the 

 data presented that — 



It will presumably be apparent that the entrance of Hypoderma larvse to 

 the bodies of the cattle takes place through the alimentary system and not 

 through the skin, and further that the larvse migrate through the oesophagus 

 and vertebral canal to the skin. 



In 1907 Jost {52) reviewed the life history of H. hovis. He con- 

 cluded that the eggs hatch in the gullet and that the larvse bore 

 through the mucous lining of it. He also makes the erroneous 

 statement that the life cycle requires about nine months. Sorensen 

 {93) in 1908 discussed the literature and concluded that the larvse 

 enter by mouth. 



During the period 1908 to 1922, Carpenter and his associates in 

 Ireland published a series of papers {12 to 19) dealing especially 

 with experiments with the muzzling of calves in an effort to prevent 

 their infestation. The earlier results were conflicting and the 

 authors changed their viewpoint from year to year. In 1914, how- 

 ever, Carpenter, Hewitt, and Reddin {17) published the results of 

 their observations on the penetration through the skin of larvse of 

 both H. lineatum and H. hovis. They first noticed soreness and 

 scabs in the regions near where eggs of Hypoderma were attached. 

 Beneath these they found holes indicating penetration and from 

 one of these was squeezed, along with serum, a first-stage larva of 

 H. lineatum which had evidently penetrated through the skin at 

 the spot. They followed this with tests of newly hatched larvse of 

 H. hovis placed on clipped hair on a calf and found that they quick- 

 ly passed down the hair and began to burrow into the skin immedi- 

 ately. They conclude : 



We believe therefore that no further doubt is possible as to the entrance of 

 young Hypoderma larvse into its host through the skin close to wherever the 

 eggs may have been laid, and the results of the muzzling experiments show 

 that entrance by the mouth is unlikely. 



