458 
Journal o f Agricultural Research 
Vol. XXIX, No. 9 
the complete cycle of development up 
to this stage requiring a minimum of 
7 days. 
(2) In liquid cultures both cuticles 
are usually retained by the larvae, 
whereas in solid cultures the first 
cuticle is cast off. Observations on 
the loss of the first skin by infective 
larvae from liquid cultures indicate 
that contact with some solid object is 
necessary for exsheathing, and that in 
a liquid medium this process does not 
ordinarily take place. 
(3) Infective larvae are only moder¬ 
ately active at room temperature, but 
may be readily stimulated to activity 
by mechanical factors. These larvae 
appear more resistant to an unfavor¬ 
able environment than do preinfective 
larvae. 
(4) Infective larvae are positively 
thermotropic and orient themselves in 
such a way that the cephalic extremity 
becomes directed to the source of heat, 
toward which the larvae swim rapidly. 
(5) In the presence of a solution of 
fuchsin the larvae behave in a manner 
unlike that observed heretofore in 
other nematode larvae. They neither 
absorb the stain and die nor do they 
exsheath, but remain alive and appar¬ 
ently unaffected by the stain, which 
after several hours’ contact with the 
larvae does not penetrate beyond the 
sheath or sheaths. 
(6) The infective larvae succumb to 
desiccation, but can maintain their 
vitality under conditions which afford 
a slight amount of moisture. 
(7) The infective larvae are posi¬ 
tively phototropic, collecting in the 
lightest portion of the culture medium. 
They also crawl up the walls of culture 
bottles, but whether the latter is to be 
interpreted as a negative geotropism 
or is due to the positive phototropism 
of the larvae is not certain. 
(8) Under experimental conditions 
the larvae show no tendency to pene¬ 
trate the skin. 
(9) Attempts made by various 
writers to correlate the behavior of 
various strongyle larvae with their skin- 
penetrating habits appear to be unten¬ 
able from the data presented in this 
paper and from data obtained by 
others. 
LITERATURE CITED 
(1) Augustine, D. L. 
1923. INVESTIGATIONS ON THE CONTROL OF 
HOOKWORM DISEASE. XIX. OBSER¬ 
VATIONS ON THE COMPLETION OF THE 
SECOND ECDYSIS OF NECATOR AMERI- 
canus. Amer. Jour. Hyg. 3: 280- 
295, illus. 
(2) Boulenger, C. L. 
1915. THE LIFE HISTORY OF NEMATODIRUS FILI- 
COLLIS RUD., A NEMATODE PARASITE 
OF THE SHEEP’S INTESTINE. Para- 
sitology 8: 133-155, illus. 
(3) Cameron, T. W. M. 
1923. ON THE BIOLOGY OF THE INFECTIVE 
LARVA OF MONODONTUS TRIGONO- 
CEPHALUS (RUD.) OF SHEEP. Jour. 
Helminthol. 1: 205-214. 
(4) CONRADI, A. F., AND BARNETT, E. 
1908. HOOKWORM DISEASE OF CATTLE (UNCI¬ 
NARIASIS). S. C. Agr. Exp. Sta. 
Bui. 137, 23 p., illus. 
(5) Dawson, C. F. 
1903. hookworms in cattle. Fla. Agr. 
Exp. Sta. Press Bui. 36, 3 p. 
( 6 ) - 
1906. SALT SICK (BOVINE UNCINARIASIS). 
Fla. Agr. Exp. Sta. Bui. 86,14 p. 
(7) Goodey, T. 
1922. A SIMPLE METHOD OF EXPERIMENTA¬ 
TION FOR SKIN INFECTION WITH 
HOOKWORM LARVAS. PrOC. Roy. 
Soc. Med. (Sect. Trop. Dis. and 
Parasitol.) 15(4): 19-20. 
( 8 ) - 
1922. OBSERVATIONS ON THE ENSHEATHED 
LARVAE OF SOME PARASITIC NEMA¬ 
TODES. Ann. Appl. Biol. 9: 33-48, 
illus. 
(9) Khalil, M. 
1922. THERMOTROPISM IN ANKYLOSTOME LAR¬ 
VAE. Proc. Roy. Soc. Med. (Sect. 
Trop. Dis. and Parasitol.) 15: 16-18. 
(10) Looss, A. 
1911. THE ANATOMY AND LIFE HISTORY OF 
AGCHYLOSTOMA DUODENALE DUB. 
A MONOGRAPH. PART 2. THE DE¬ 
VELOPMENT IN THE FREE STATE. 
Egypt Ministry Ed., Rec. School 
Med. 4:159-613, illus. 
(11) Ortlepp, R. J. 
1923. THE LIFE-HISTORY OF SYNGAMUS TRA- 
CHEALIS (MONTAGU) V. SIEBOLD, 
THE GAPE-WORM OF CHICKENS. 
Jour. Helminthol. 1: 119-140, illus. 
(12) Ransom, B. H. 
1906. THE LIFE HISTORY OF THE TWISTED WIRE 
WORM (HAEMONCHUS CONTORTUS) 
OF SHEEP AND OTHER RUMINANTS. 
U. S. Dept. Agr. Bur. Anim. 
Indus. Circ. 93, 7 p., illus. 
(13) Reisinger, L. 
1916. BEITRAG ZUR ANKYLOSTOMIASIS DES 
rindes. Wiener TierSrztl. Mon- 
atsschr. 3: 467-487, illus. 
(14) Stiles, C. W. 
1901. VERMINOUS DISEASES OF CATTLE, 
SHEEP, AND GOATS IN TEXAS. U. S. 
Dept. Agr. Bur. Anim. Indus. 
Ann. Rpt. (1900) 17: 356-379. 
(15) Veglia, F. 
1915. THE ANATOMY AND LIFE-HISTORY OF 
THE HAEMONCHUS CONTORTUS 
(rud.). Union South Africa Dept. 
Agr. Rpt. Director Vet. Research 
3/4 : 347-500, illus. 
