62 EXPERIMENTAL RESEARCHES 



stances permitting proliferation of the spiro- 

 chaetae must be present. Probably there exists 

 only a minimum of such substances, auxiliary, 

 but indispensable for their nutrition. 



I may here remind you of the fact that the 

 influenza bacillus, as was shown by R. Pfeiffer, 

 is not able to proliferate in ordinary culture 

 media, but that a trace of haemoglobin is neces- 

 sary for its growth. In syphilis I imagine the 

 case to be somewhat similar. All the organs 

 which can be primarily infected with syphilitic 

 virus would thus be the carriers of this specific 

 auxiliary substance. 



The case is more evident, macroscopically, in 

 a great number of very different affections, e.g., 

 variola and vaccinia, bird's and sheep's pox, 

 foot- and mouth-disease, trachoma, rabies, 

 fowl's pest and scarlatina. In all these infec- 

 tions there are found in the epithelial cells the 

 above-mentioned peculiar cell-inclusions, which 

 in small-pox are called Guarnieri's corpuscles, in 

 rabies Negri's corpuscles. According to recent 

 investigations we are justified in supposing that 

 these inclusions do not themselves represent the 

 parasites, but that they are derived from the 

 cells and consist, according to von Prowazek, of 

 plastin and nuclease. Within these masses 



