METHODS OF EXAMINATION 425 



times larger. Cantani therefore concludes that the brain 

 substance is the most suitable nidus for their growth, but 

 agrees with Pfeiffer in believing that the chief symptoms are 

 produced by toxins resident in the bodies of the bacilli. He 

 made control experiments by injecting other organisms, and also 

 by injecting inert substances into the cerebral tissue. 



The evidence, accordingly, that the influenza bacillus is the 

 cause of the disease rests chiefly on the well-established fact that 

 it is always present in the secretions of the respiratory tract in 

 true cases of influenza, and often in very large numbers. The 

 observed relationships of the organism to lesions in the lungs 

 and elsewhere leave no room for doubt that it is possessed of 

 pathogenic properties, but we cannot yet maintain that its causal 

 relationship to epidemic influenza is absolutely established. A 

 certain amount of confirmatory evidence has been supplied by 

 the results of experiment. 



Methods of Examination (a) Microscopic. A portion of the 

 greenish-yellow purulent material which often occurs in little 

 round masses in the sputum should be selected, and film prepara- 

 tions should be made in the usual way. Films are best stained 

 by Ziehl-Neelsen carbol-f uchsin diluted with ten parts of water, 

 the films being stained for ten minutes at least. In sections of 

 the tissues, such as the lungs, the bacilli are best brought out, 

 according to Pfeiffer, by staining with the same solution as above 

 for half an hour. The sections are then placed in alcohol 

 containing a few drops of acetic acid, in which they are 

 dehydrated and slightly decolorised at the same time. They 

 should be allowed to remain till they have a moderately light 

 colour, the time varying according to their appearance. They 

 are then washed in pure alcohol, cleared in xylol, and afterwards 

 mounted in balsam. 



(b) Cultures. A suitable portion of the greenish -yellow 

 material having been selected from the sputum, it should be 

 washed well in several changes of sterilised water. A portion 

 should then be taken on a platinum needle, and successive 

 strokes made on the surface of blood-agar tubes. The tubes 

 should then be incubated at 37 C., when the transparent 

 colonies of the influenza bacillus will appear, usually within 

 twenty-four hours. These should give a negative result on 

 inoculation on ordinary agar media. 



PLAGUE. 



The bacillus of oriental plague or bubonic pest was discovered 

 independently by Kitasato and Yersin during the epidemic at 



