456 
Journal of Agricultural Research 
Vol. XXIX, No. 9 
under the cover glass, the current thus 
set up acting as a stimulant to activity, 
(2) by applying heat, (3) by watching for 
spontaneous signs of activity, which 
usually occur at variable intervals. 
Throughout this series of observations, 
involving a number of larvae, one larva 
showed evidence of having absorbed 
some stain, but it had lost its vitality 
and showed no response to stimulation. 
Cameron (3) states that the larvae 
of Monodontus trigonocephalus when 
treated with fuchsin absorb the stain 
rapidly and die, in contrast to the be¬ 
havior of the larvae of Ancylostoma 
duodenale, which fail to absorb the 
stain and escape from their sheaths, 
which alone become stained, as shown 
by Looss (10) and by other investiga¬ 
tors. Cameron also states: “Goodey 
(8) showed that this was also true for 
Necator larvae; but that Haemonchus 
and Graphidium which do not pene¬ 
trate the skin, absorbed the stain and 
died.” He further states that all skin 
penetrators that have been tested ex- 
sheathed, whereas nonskin penetrators 
have not exsheathed but died when 
treated with stain. In Goodey’s paper 
to which Cameron refers the only 
statements concerning reaction of nem¬ 
atode larvae to stains are the follow¬ 
ing: “I found that N. americanus larvae 
come out of their sheaths, as found by 
Herman and confirmed by Looss, when 
the drop containing the larvae and stain 
is covered with a cover slip. G . 
strigosum and T. retortaeformis larvae 
did not exsheath.” Nowhere in 
Goodey’s paper are there any refer¬ 
ences to the behavior of Haemonchus 
larvae in the presence of stain or any 
reference to the fact that the larvae of 
Graphidium and Trichostrongylus were 
killed by stains (methyl green and 
fuchsin). 
In the present writer’s experiments 
Bustomum larvae did not exsheath in 
the presence of fuchsin, nor coil up and 
die. As will be shown later, there is no 
necessary correlation between the re¬ 
action of larvae to stains and their 
ability to penetrate skin. 
EFFECTS OF DRYING 
According to Conradi and Barnett 
(4), infective larvae of Bustomum phle- 
botomum are resistant to drought, but 
according to the writer’s observations 
infective larvae of Bustomum phleboto- 
mum are not resistant to drying. Slide 
preparations with and without cover 
glasses containing larvae were allowed 
to dry at room temperature for periods 
varying from one to several hours. 
After being moistened it was found 
that the larvae were retracted in their 
sheaths, and although the retracted 
larvae absorbed water, as a result of 
which they gradually filled out the 
empty spaces in the cuticle, they did 
not regain their vitality. These obser¬ 
vations were made during the winter 
months in a steam-heated laboratory 
having a very low humidity content, 
and were repeated a number of times 
with similar results. Although the 
larvae are not resistant to drying, 
they can maintain their vitality for a 
long time in the presence of a small 
amount of moisture. Thus a solid- 
culture medium in a covered Petri dish 
to which water had not been added for 
about three weeks and which had the ap¬ 
pearance of being dry yielded larvae 
many of which had retained their 
vitality and exhibited lively move¬ 
ments after being moistened. 
Nematode larvae exhibit considerable 
variation in resistance to drying. Ran¬ 
som (12) showed that the larvae of 
Haemonchus contortus are highly re¬ 
sistant to drying, and that they can be 
revived after 35 days’ exposure to 
drying. Looss (10) found that the 
larvae of Ancylostoma duodenale shrivel 
up and die when the moisture evapo¬ 
rates from their bodies. Boulenger (2) 
showed that Nematodirus larvae are 
resistant to drying, and this observa¬ 
tion has been confirmed by Cameron 
( 8 ). 
Goodey (8) confirms Looss’s obser¬ 
vation for Necator americanus and 
states: “It seems a natural inference 
to draw therefore that Necator and 
Ancylostoma seek the protection af¬ 
forded by penetration into the skin 
because if they remained outside and 
became dry they would perish.” The 
same writer found that the larvae of 
Graphidium strigosum and of Tricho¬ 
strongylus retortaeformis can withstand 
ordinary desiccation at room tempera¬ 
ture for a few days and revive on the 
addition of water, behaving in this 
respect like the larvae of Haemonchus 
contortus as shown by Ransom (12) 
and confirmed by Veglia (IS). Came¬ 
ron (3) found that the larvae of Mono¬ 
dontus trigonocephalus offer little resist¬ 
ance to drying, and since these larvae 
are not skin penetrators, it is unsafe 
to attempt to correlate susceptibility 
to drying with the habit of boring 
through the skin. The present writer’s 
observations with reference to the 
behavior of the larvae of Bustomum 
phlebotomum , which do not penetrate 
the skin under experimental condi¬ 
tions, lend no confirmation to the view 
that nonskin penetrators are resistant 
to drying. 
