Nov. 1, 1924 
Preparasitic Stages of the Cattle Hookworm 
457 
REACTION TO LIGHT 
The ensheathed larvae of Bustomum 
phlebotomum are positively phototropic, 
as the following observations will show. 
In a 14-day-old culture on a char- 
coal-and-feces mixture larvae were 
found along the walls of the bottle 
facing the light of a north window, 
but none was found along the walls 
of the bottle facing the room. In a 
10-day-old culture w T hich was kept in 
a dark place no larvae were found 
along the walls of the bottle, whereas 
in a culture made from the same lot 
of worms but kept near the window' 
larvae were found crawling up the 
walls of the bottle facing the light. 
Similar observations made at various 
times on larvae in cultures indicate 
that they respond positively to light 
by collecting in parts of culture dishes 
exposed to light and by being absent 
from shaded portions. 
In their light reactions the larvae 
of Bustomum phlebotomum resemble the 
larvae of Monodontus (Cameron, 3) 
and Haemonchus contortus (Veglia, 15). 
REACTION TO GRAVITY 
Conradi and Barnett (4) noted that 
the larvae of Bustomum phlebotomum 
crawl up the walls of culture jars. 
The present writer’s observations bear 
out this point. Whether this upward 
movement of the larvae is a negative 
geotropism or whether it is merely an 
expression of their positive phototro- 
pism is not clear from the data at hand. 
The tendency of the larvae to climb up 
the walls of culture dishes, and their 
presumably similar tendency to climb 
up blades of grass and other objects 
in nature, is doubtless an adaptation 
to secure an advantageous position in 
order to complete their life cycle. 
Ransom {12) pointed out the adapta¬ 
tion of the upward migration of 
Haemonchus and other strongyle 
larvae to the feeding habits of rumi¬ 
nants, which favors the ingestion of 
the larvae by the host. Similar tend¬ 
encies have been observed in most 
larvae belonging to the superfamily 
Strongyloidea, Syngamus, according 
to Ortlepp (11) } and Monodontus, ac¬ 
cording to Cameron (3), being excep¬ 
tions. 
EXPERIMENTS ON SKIN PENETRATION 
In 1919 infective larvae of Bustomum 
phlebotomum were placed on the skin of 
guinea pigs, the area on which the lar¬ 
vae were placed having been previously 
shaved. In the course of several 
experiments no local skin reaction was 
observed in these experimental animals, 
and intact larvae were recovered from 
the skin. Later, experiments were 
made in accordance with the method 
devised by Goodey (7) . Skin from a 
7-day-old rat was stretched on a thin 
sheet of cork in the center of which 
was a hole about an inch in diameter, 
and the cork was floated in physio¬ 
logical salt solution in a glass dish kept 
in an incubator at a temperature of 
37°. A drop of water containing a 
number of larvae was placed on the 
skin. Repeated examinations showed 
the larvae on the surface of the skin. 
The larvae were sucked up in a pipette 
and examined from time to time on a 
glass slide. There was no evidence of 
their having molted. After the experi¬ 
ment had been in progress several 
hours the drop of water on the rat’s 
skin containing the larvae was allowed 
to evaporate. A drop of distilled 
water was added to the skin and the 
larvae were sucked up in a fine pipette 
and examined microscopically. They 
were nearly all active. The skin was 
then fixed in 70 per cent alcohol and 
cleared in lactophenol. Microscopic 
examination of the cleared skin failed 
to show any evidence of penetration 
by the larvae. 
Cameron (5) has shown that the lar¬ 
vae of a related hookworm {Monodontus 
trigonocephalus) do not penetrate the 
skin under experimental conditions. 
Since well-known skin penetrators 
(Ancylostoma and Necator) penetrate 
the skin under similar experimental 
conditions, this method may be con¬ 
sidered a reliable test of the ability of 
nematode larvae to bore into the skin. 
Assuming, therefore, that the results 
obtained by Cameron {3) with the 
larvae of Monodontus and the results 
obtained by the present writer^ with 
Bustomum give reliable information as 
regards the inability of the larvae of 
these genera to penetrate the skin, it 
is evident from the data and discussion 
presented in the foregoing pages that 
attempts of various investigators to 
establish correlations between behavior 
of nematode larvae and their probable 
mode of entry into the host is untenable. 
SUMMARY 
(1) Under laboratory conditions at a 
temperature of 70° to 80° F. the eggs 
of Bustomum phlebotomum hatch in 
about 96 hours. The first-stage larvae 
are found in lethargus 24 hours after 
hatching, and 24 hours later the second 
lethargus is in progress. After a 
second lethargus, which lasts at least 
24 hours, third-stage larvae emerge, 
