Nov. 1, 1924 
Preparasitic Stages of the Cattle Hookworm 
455 
portion of the body concealed under 
some solid object and the rest of the 
body straight and rigid are usually 
seen in culture dishes and cover-glass 
preparations. 
Infective larvae appear generally 
more tolerant of an unfavorable en¬ 
vironment than are preinfective larvae. 
Preinfective larvae are easily killed in 
culture dishes when bacteria are 
present in large numbers, the heaviest 
mortality occurring during the leth- 
argus. But infective larvae were found 
in culture media containing massive 
bacterial growths. While preinfective 
larvae can maintain their vitality at a 
low temperature, they frequently de¬ 
generate in a refrigerator, whereas 
this phenomenon was not observed in 
infective larvae, which were kept at 
8° C. in water without showing any 
signs of degeneration. Infective larvae 
were also frozen solid for about 15 hours 
outside of a window, and after being 
thawed they gradually resumed, their 
normal shape and became active, 
showing what appeared to be a com¬ 
plete recovery in about 5 hours, where¬ 
as preinfective larvae are easily killed 
by cold, according to Conradi and 
Barnett (4). Ransom (12) showed 
that the preinfective larvae of Hae - 
monchus contortus offer comparatively 
little resistance to freezing, although 
infective larvae could be frozen and 
successively thawed out many times. 
REACTION TO HEAT 
Under the influence of heat the 
larvae exhibit very lively movements. 
Thus, if the point of a needle heated in 
a flame or the heated end of a glass rod 
is brought into contact with the under¬ 
surface of a glass slide containing 
larvae, they become very active and 
orient themselves toward the source 
of the heat, moving very rapidly in that 
direction. The orientation of the larvae 
with reference to the source of heat is 
unfailing, and the writer took ad¬ 
vantage of this reaction to concen¬ 
trate larvae in the center of a dish in 
which comparatively few larvae were 
present. Holding a hot glass rod 
against the outer surface of the bottom 
of a Petri dish caused the larvae to 
collect in a circumference around the 
point to which heat was applied, ap¬ 
proaching thither from all directions. 
While heat is an unfailing source of 
stimulation to the larvae, it was noted 
that larvae which collected near the 
edge of a drop of water on a slide, a 
tendency which they frequently ex¬ 
hibit, do not orient themselves toward 
the source of heat but merely exhibit 
feverish activity by vigorous and 
spasmodic movements of the body, 
without turning the cephalic extremity 
which continues to be in contact with 
the periphery of the drop. 
If too much heat is applied the larvae 
cease their movements before they 
reach the source of heat, coiling up 
instead and resuming their activities as 
the heat diminishes. 
Khalil (9) showed that the infective 
larvae of a number of nematodes are 
positively thermotropic. He obtained 
positive results with Ancylostoma duo- 
denale, Necator americanus, Ancy¬ 
lostoma ceylanicum, Strongyloides 
stercoralis , Galoncus perniciosus, and 
Trichostrongylus douglasi, and nega¬ 
tive results with Haemonchus contortus. 
As Haemonchus contortus is not a skin 
penetrator, Khalil concluded that only 
skin penetrators are positively thermo¬ 
tropic. Recently Cameron (3) showed 
that Monodontus trigonocephalus is 
positively thermotropic, although the 
larvae do not penetrate the skin under 
experimental conditions identical with 
those under which Ancylostoma cey¬ 
lanicum penetrates it. As will be 
shown later, Bustomum phlehotomum 
does not penetrate the skin under ex¬ 
perimental conditions, thus affording 
further evidence that there is no cor¬ 
relation between positive thermo¬ 
tropism and ability of larvae to pene¬ 
trate the skin. In this connection it 
may be of interest to note that the 
larvae of Nematodirus are negatively 
thermotropic according to Cameron's 
observations ( 3 ). 
REACTION TO STAIN 
The reaction of the infective larvae 
to stain was studied by allowing a 1 
per cent solution of basic fuchsin to 
run in under cover-glass preparations 
containing larvae. As the stain runs in 
the larvae are active at first; but that 
this activity is independent of the 
stain and is due to the current can be 
readily shown by running in water 
under the cover-glass. As the larvae 
become enveloped in stain they gener¬ 
ally become quiescent but do not ab¬ 
sorb the stain. Larvae were kept under 
observation for several hours (6 hours 
in one case and 3 hours in two other 
cases), but no penetration of the stain 
into the tissues of the larvae was ob¬ 
served. The stain readily penetrates 
the sheath, as is seen distinctly when¬ 
ever a larva retracts within the sheath, 
but the writer found no evidence of 
penetration of the stain beyond that 
point. The larvae remained in the 
stain for hours without loss of vitality. 
Their vitality while quiescent can be 
demonstrated (1) by running water 
