450 THE HEMORRHAGIC SEPTICEMIA GROUP 
observed in the tissues of animals. The total dimensions under such 
circumstances are 0.3 to 0.5 micron in diameter and 0.4 to 1 micron in 
length. Coccoid forms are commonly found in smears from animal 
tissues. It is non-motile, and no spores have been demonstrated. It 
stains with difficulty: ordinary stains, even carbol-fuchsin, are usually 
ineffective, but the stronger dyes, as gentian violet, and Victoria blue 
dissolved in anilin, color it faintly but distinctly. There is a tendency 
toward bipolar staining. 
Cultivation.— Ordinary cultural mediums do not support growth. 
McCoy and Chapin found coagulated egg yolk a good medium, and 
Francis has shoAvn that the richer mediums, as blood-agar or serum-agar, 
enriched with a piece of sterile fresh rabbit liver^ are also satisfactory. 
The growth is rather restricted, smooth, colorless, glistening and 
viscid, but otherwise not distinctive. 
Products of Growth. — Pmzymes, toxins or any other significant pro- 
ducts of growth have not been reported. 
Pathogenesis for Man. — Several accidental laboratory infections- 
afford evidence of the pathogenicity of Bacterium tularjense for man. 
The disease thus induced was characteristic in each case. 
Pathogenesis for Animals.— Rabbits, guinea-pigs, white rats and 
ground squirrels are readily infected either from the blood of human 
cases at the height of the disease, from pus obtained from suppurating 
foci, or from enlarged lymph glands, as well as from the liver or spleen 
of animals exliibiting either the naturally occurring, or artificially 
induced disease. The autopsy shows caseation of lymph glands, and 
small necrotic foci in the liver and spleen, and in general the parenchy- 
matous organs. 
The cat, dog, goat, calf, and pigeon are naturally immune. 
The disease does not seem to spread from animal to animal by 
contact: rather the virus is transmitted by blood-sucking insects. 
Francis induced the disease in rabbits through the agency of infected 
horseflies (Chrysops discalis^), the rabbit louse (Hpemodipsus ventri- 
cosus^), the bed bug (Cimex lectularius^), the mouse louse (Polypax 
serratus^), and the wood tick (Demacentor andersoni^). The observa- 
tions of Parker and Spencer^ that the organism may be transmitted 
from adult ticks through the egg to the progeny is important in that it 
indicates a methofl of propagation of the bacterium through an insect 
as well as from animal to animal, and of great biological significance 
in that it is apparently one of a very few instances in which a patho- 
genic microbe is inheritable through a series of insect hosts. Of 
1 Francis: Public Health Reports, 1922, 37, 102. 
2 See Lake and Francis: Ibid., 1922, 37, 392. Freese, Lake and Francis: Ibid., 
1926, 41, 369. 
3 Public Health Reports, 1921, 36, 1738. -t Ibid., p. 1747. 
s Ibid., 1922, 37, 83. ''> Ibid., 37, 96. 
■ Ibid., 1924, 39, 1057. It will ba recalled that Rocky Mountain spotted fever is also 
transmissible through the wood tick. 
8 Public Health Reports, 1926, 41, Nos. 27 and 28. 
