EXPERIMENTAL INOCULATION 483 



bacteria. Some of the examples are a. little larger than the influenza 

 bacillus, and tend to form short filaments, but others are quite indis- 

 tinguishable. Most 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. He accordingly 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. In the case of 

 rabbits, intravenous injection of living cultures produces dyspnoea, 

 muscular weakness, and slight rise of temperature ; death may 

 follow. Wollstein distinguishes virulent and avirulent types 

 according to the result on intravenous injection in the rabbit ; the 

 virulent types cause death in about twenty-four hours, the bacilli 

 being numerous in the blood. The dose used, however, is com- 

 paratively large, namely, a blood-agar culture for a rabbit of 1000 

 grammes. Strains from the respiratory tract were non-virulent 

 by this test ; those from the blood and meninges, and rarely 

 from pneumonic lung, were virulent. No essential difference 

 between the strains was brought out by serological tests. 

 Wollstein has found that a fatal cerebro-spinal meningitis can 

 be produced in monkeys by the sub-dural injection of virulent 

 cultures ; and that, in certain circumstances, this affection may 

 be cured by means of an anti-influenza serum obtained from 

 the goat. 



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 concluded that the brain substance is the most suitable 

 nidus for their growth, but agreed with Pfeiffer in believing that the 



