4 io INFLUENZA. 



injection of dead cultures, though in this case the dose 

 required to be five or six 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 toxines 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 that it is an 

 organism which has not been found in any other condition. 

 Moreover, it is an organism which is practically restricted 

 by its conditions of growth to the animal body. 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 preparations should be made in the usual way. 

 Films are best stained by Ziehl-Neelsen carbol-fuchsin 

 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 placed 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. 



