EXPERIMENTAL INOCULATION 471 



(p. 472). Miiller's "trachoma bacillus" (p. 219) is a member of 

 the same group. All these organisms are very restricted in their 

 growth, and require the addition of blood or haemoglobin to the 

 ordinary culture media ; hence they are sometimes spoken of as 

 hamiophilic bacteria. Some of the examples are a little larger 

 than the influenza bacillus, and tend to form short filaments, 

 but others are quite indistinguishable. All of them also seem to 

 have very feeble pathogenic properties towards the lower animals. 

 At present it can scarcely be claimed as possible to identify 

 Pfeiffer's bacillus by its microscopic and cultural characters. 



Experimental Inoculation. --There is no satisfactory evidence 

 that any of the lower animals suffer from influenza in natural 

 conditions, and accordingly we cannot look for very definite 

 results from experimental inoculation. Pfeiffer, by injecting 

 living cultures of the organism into the lungs of monkeys, in 

 three cases produced a condition of fever of a remittent type. 

 There was, however, little evidence that the bacilli had under- 

 gone multiplication, the symptoms being apparently produced 

 by their toxins. In the case of rabbits, intravenous injection of 

 living cultures produces dyspnoea, muscular weakness, and 

 slight rise of temperature, but the bacilli rapidly disappear in 

 the body, and exactly similar symptoms are produced by 

 injection of cultures killed by the vapour of chloroform. 

 Pfeiffer, therefore, came to the conclusion that the influenza 

 bacilli contain toxic substances which can produce in animals 

 some of the symptoms of the disease, but that animals are not 

 liable to infection, the bacilli not having power of multiplying 

 to any extent in their tissues. 



Cantani succeeded in producing infection to some extent in rabbits, by 

 injecting the bacilli directly into the anterior portion of the brain. In 

 these experiments the organisms spread to the ventricles, and then 

 through the spinal cord by means of the central canal, afterwards in- 

 fecting the substance of the cord. An acute encephalitis was thus pro- 

 duced, and sometimes a purulent condition in the lateral ventricles. 

 The bacilli were, however, never found in the blood or in other organs. 

 Similar symptoms were also produced by 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 Pfeirl'er in believing that the 

 chief symptoms are produced by toxins resident in the bodies ol 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 



