456 HEMOGLOBINOPHILIC BACILLI 
insufflation of cultures of the Pfeiffer bacillus, but the disease lacks 
many of the characteristics of the influenzal pneumonia. Xicolle 
and Lebaillyi have reported the successful infection of monkeys (genus 
Macacus) with mucus from influenza cases diluted with salt solution 
and passed through Chamberland filters. Gibson, Bowman and 
Connor- have made similar experiments which would appear to confirm 
this work, in so far as their limited observations have shown. These 
experiments suggest the possibility that a filterable virus obtained 
from human cases of influenza will induce influenza or an influenza-like 
disease in certain kinds of monkeys. Viewed in the light of the exten- 
sive negative attempts to transmit the disease from man to man by 
American observers,^ they leave the etiology of influenza still a subject 
of controversy. Attempts to induce immunity in experimental animals 
by injections of influenza bacilli have been unsuccessful. 
Immunity.— The extent and duration of immunity following recovery 
from an attack of influenza is problematical. On the one hand, relapses 
are not infrequent, but, on the other hand, a majority of those who 
convalesce from an infection in the primary wave of an epidemic of the 
disease fail to become infected during the succeeding secondary waves 
which so characteristically follow. 
Leishman^ has reported statistics from the British Expeditionary 
Forces which would suggest that prophylactic vaccination with the 
Pfeiffer bacillus confers some resistance to subseciuent infection. The 
figures follow: 
Number of Incidence Lung 
men. of attack. complications. Deaths. 
Inoculated 15,624 14.1 0.12 
Uninoculated 43,520 47.3 2.25 
Similar attempts at immunization in the United States have given 
irregular results. Upon the whole, the evidence of protection against 
influenza by vaccination with the Pfeiffer bacillus is inconclusive in the 
light of current information. 
Bacterial Identification of Bacillus Influenzae. — 1 . Sputum raised from 
the deeper air passages is spread upon slides, air dried, fixed, and 
stained with dilute carbol-fuchsin. Large numbers of minute organ- 
isms colored pink, with a tendency toward bipolar staining, are sugges- 
tive of the influenza bacillus. There is no tendency toward a definite 
arrangement of the bacilli. They are frequently found in leukocytes. 
2. r?//^?/ro/.— Blood-agar plates are made by depositing a generous 
drop of human, rabbit or pigeon's blood in the center of an agar plate. 
A better medium is the oleate erythrocyte agar of Avery. Mucus 
raised from the deeper air passages is thoroughly Avashed in sterile 
water and emulsified in broth or water, selecting for the purpose 
1 Compt. rend. Acad. Sci., 1918, 167, 607; Ann. Inst. Pasteur, 1919, 33, 395. 
2 British Med. .Jour., 1918. ii, 645. 
3 Public Health Reports, 1919, 34, 33. 
^ .Tour. Am. Med. Assn., 1920, 74, 814. 
