332 
The War ble-flies of Cattle 
muzzling that they were inhibited from licking themselves during the fly- 
season. The earlier experiments were invalidated, either through faulty muzzles 
or from the difficulty of subjecting muzzled and free animals to precisely the 
same conditions, and for some years the results were conflicting. Improved 
methods, however, gave a distinct indication that muzzling did nothing to 
decrease the number of warbles but even tended to increase them, the inference 
being that such eggs or larvae as were licked off came to nothing. This con¬ 
clusion was arrived at about 1912, and in 1914 Carpenter and Hewitt remarked 
that the newly discovered first-stage larva was as well adapted for perforating 
the skin as the wall of the gullet. 
Further negative evidence was obtained by feeding eggs and newly hatched 
larvae to calves never exposed to fly attack. In 1913 Carpenter and Hewitt 
fed 16 newly laid eggs of H. bovis to each of three calves, and in 1914 a similar 
experiment was tried with newly hatched larvae, but no warbles resulted. 
In 1913 Glaser placed newly hatched larvae on a shaved patch on the skin 
of a calf, but observed no attempt at penetration. In 1914, Carpenter, Hewitt 
and Reddin were more fortunate. “Instead of shaving we clipped closely a 
small patch on the shoulder of a black calf, thus keeping the conditions more 
nearly normal, and put seven maggots on it... . Immediately they were put 
on the hairs they crawled down them to the skin, and directed their bodies 
perpendicular to its surface. We soon found that they were disappearing slowly 
into the skin; four were lost sight of, but the other three were watched cutting 
the epidermis with their mouth-hooks and occasionally bending the hinder 
region of their bodies until they disappeared completely. It took them about 
six hours to get into the skin; possibly hair follicles may have facilitated their 
entrance.” The uneasy movements of the calf made it very difficult to observe 
exactly the movements of these minute semi-transparent larvae. 
In April 1915 Had wen made several successful experiments with the first- 
stage larvae of H. lineatum, by placing them on small pieces of skin freshly re¬ 
moved from a cow. Their attempts at penetration could be followed at ease 
under the microscope, and though the condition of the skin of course rapidly de¬ 
teriorated, despite the arrangements to keep it constantly moistened,many suc¬ 
ceeded in half burying themselves, and a few entirely disappeared. On May 7 a 
piece of skin underlying three hairs to which twelve eggs were attached was re¬ 
moved from a cow. At the foot of one of the hairs a small droplet of clear serum 
was exuding, which kept increasing in size. By doubling the skin and squeezing, 
Hadwen expressed two larvae, one of which made determined efforts to re¬ 
enter the hair follicle. Carpenter, Hewitt and Reddin had a similar experience. 
As to the actual procedure of the larva, Hadwen writes: 
Upon emerging from the egg the larva crawls actively along the hair to the skin. It is 
apparently aided in this by a sticky exudate with which it is covered, and which seems also 
to serve the purpose of preserving it from drying out. Upon reaching the root of the hair it 
begins to work with its mouth-parts. In no instance was a larva observed to penetrate the 
skin otherwise than by a hair follicle. The adherence of the larva to the hair keeps it in proper 
position for penetration and provides it with a point d’appui. 
