TULAREMIA AND BACTERIUM TULAR.ENSE 451 
especial significance, also, is the readiness with which experimental 
animals, and very probably man, may become infected through 
abrasions of the skin. Even very minute cutaneous cuts may afford 
a portal of entry for the organism: indeed, a method of obtaining pure 
cultures of Bacterium tularaense from mixtures of bacteria is to rub 
some of the material upon the shaved abdomen of a guinea-pig with a 
clean glass rod. Infection takes place much in the same manner that 
plague infection occurs under similar conditions. 
Immunity.— Very little is known about immunity to tularemia but 
Francis reports a second infection in a person who imdoubtedly had a 
typical case of the disease two years and five months after his first 
attack. The second attack was quite mild, and there were almost no 
generalized symptomatology, however. 
Bacteriological Diagnosis. — 1. Isolation and Identification of Bacter- 
ium T idarcense.—CvXtVirQS are made from the suspected blood, or pus, 
or organs from autopsy upon the coagulated egg-yolk medium, or 
upon blood- or serum-agar enriched with a piece of sterile rabbit liver. 
The shining mucoid growth, while not distinctive, and the difficulty 
of staining, even with powerful dyes dissolved in anilin oil, is suggestive. 
2. Animal I noc7dation. Suspected material rubbed on the shaved 
abdomen of a guinea-pig usually leads to a fatal infection with rather 
distinctive pathology. 
3. Agglutination Reaction.— Vsu&Wy the blood serum of a well- 
developed case in man will agglutinate standard cultures of Bacterium 
tularwnse. The titer of such sera varies from 1 to 10 to 1 to 1200. 
Usually a dilution of 1 to 50 will show clumping. 
Francis and Evans^ have made the very important observation that 
not infrequently serums that agglutinate Bacterium tularfense will 
also agglutinate B. abortus and Bacillus melitensis. Sometimes the 
titer of the serum reaches an equal, or nearly equal value for tular- 
ense on the one hand, and abortus and melitensis on the other hand. 
More commonly, the homologous organism exhibits the highest titer. 
It is necessary, therefore, to make parallel agglutination tests upon 
sera from cases that suggest tularemia, using the three organisms 
respectively, unless the clinical history is unequivocal. If, then there 
is a differential titer for tularense, the case may be diagnosed. If, on 
the contrary, the titer is about equal for the three organisms an agglu- 
tination absorption test should be performed to determine the specific 
organism. 
Complement-fixation has been described by Francis,-' but at present 
this procedure is not as practical as the methods of animal inoculation 
and agglutination tests. 
Prevention of Tularemia.— The usual mode of infection of man by 
Bacterium tularsense is through handling infected rabbits. Human 
infection through the bite of an insect is thus far quite rare. It follows 
that the careful inspection of game offered for sale during the ojien 
season should afford adequate protection against this disease. 
1 Public Health Reports, 1922, 37. 393. 2 Ibid. 
