EXPERIMENTAL INOCULATION 505 



in 1897-8 Besson only found the organism in 80 per cent, of cases investigated. 

 Achalme, Rosenthal, Bezan9on, and others have reported similar observations. 

 Again, Pfeiffer's bacillus or an organism like it has been found in healthy 

 persons as well as in cases of whooping cough, broncho-pneumonia, etc. 



Relying on these negative observations many authors have raised a doubt as to 

 the specific relationship of Pfeiffer's bacillus to influenza. Rosenthal, for instance, 

 comes to the conclusion that " the haemophilic cocco-bacillus (or bacillus of Pfeiffer} 

 is a micro-organism commonly found among the pathological flora of the lung, and 

 is not the bacillus which causes influenza." But the known persistence of Pfeiffer's 

 bacillus in chronic lesions of the lung offers quite a satisfactory explanation of 

 the occurrence of the organism among the flora of phthisical cavities, tuberculous 

 bronchitis, etc., and is in no way inconsistent with the specific relationship of 

 the bacillus to influenza. Further, there is no apparent reason why, under certain 

 circumstances, Pfeiffer's bacillus should not live as a saprophyte in the human 

 tissues : it is well known that the pneumococcus, the diphtheria bacillus and other 

 organisms are frequently found under such conditions, and no question is ever raised 

 as to the specific relationship of these organisms to their respective diseases. Again 

 new haemophilic micro-organisms similar to or identical with Pfeiffer's bacillus are 

 being constantly described, e.g. the organisms found by Jochmann and Moltrecht 

 in whooping cough, by Wolff in rats, and by Friedberger in dogs. Hence, it would 

 appear that there is a group of haemophilic micro-organisms, of which Pfeiffer's 

 bacillus is the type, which inhabit for preference the respiratory passages but exhibit 

 very divergent pathogenic properties. 



Ancillary micro-organisms. In influenza, particularly in the pulmonary 

 lesions, Pfeiffer's bacillus is frequently accompanied by other pathogenic 

 organisms, the more common being pneumococci and various streptococci. 

 Reference will be made to these associated micro-organisms later but mean- 

 while it may be said that they largely determine the severity of the disease. 



SECTION I. EXPERIMENTAL INOCULATION. 



As a result of his observations, Pfeiffer came to the conclusion that with 

 the exception of monkeys the lower animals are immune against Pfeiffer's 

 bacillus. This natural resistance may, however, be overcome by experi- 

 mental methods. 



Monkeys. The inoculation of a pure culture of Pfeiffer's bacillus, or of 

 sputum from cases of influenza, into the trachea, lung or nasal fossae of 

 monkeys is followed by a disease with symptoms similar to those of influenza 

 in man. As a rule the animal recovers. In one fatal experiment, the pul- 

 monary lesions were very like those seen in the human disease ; the bacillus 

 was found in this case in small numbers in the blood, bronchial secretions, 

 and pulmonary mucus (Pfeiffer). 



Laboratory animals. Rats, pigs, cats, dogs, and pigeons are absolutely 

 immune. 



Rabbits. The inoculation of large doses of pure cultures into the ear vein 

 of a rabbit is sometimes fatal. Two or three blood-agar cultures emulsified 

 in broth should be used. Under these conditions the organism does not 

 generally multiply in the tissues but the animal dies from the effects of the 

 soluble products inoculated at the same time as the organism. 



This, and the fact that cultures killed with chloroform are equally fatal, tends to 

 show that death is the result of an intoxication and not of an infection. Pfeiffer 

 never obtained in any species of animal but monkeys " a multiplication of the 

 inoculated bacilli, that is, a true infection." 



It is nevertheless possible to produce an infection in rabbits. Thus, 

 Meunier and also Elmassian produced a fatal infection in rabbits by intra- 



