TRANSMISSION OF THE DISEASE TO ANIMALS 523 



eye of the rabbit is susceptible to inoculation from syphilitic 

 lesions. The material used is introduced in a finely divided 

 state either into the tissue of the cornea or into the anterior 

 chamber, and syphilitic keratitis or iritis, or both, may result, 

 there being a period of incubation of at least two weeks. 

 Levaditi and Yamanouchi have studied the stages in detail, and 

 find that the spirochsetes remain in the inoculated material un- 

 changed for a time ; then organisation occurs and the spirochsetes 

 multiply, and later still there is a more rapid multiplication and 

 invasion by them of the tissues of the eye. The period of incu- 

 bation is thus not due to the organism passing through some 

 cycle of development, but simply to its requiring certain con- 

 ditions for multiplying which are not supplied for some time. 

 The testis of this animal is also a convenient site of inoculation, 

 a syphilitic orchitis being set up, and the disease has been 

 maintained by this method through several generations of 

 animals. Uhlenhuth and Mulzer produced generalised syphilitic 

 lesions in young rabbits by intracardiac inoculation with syphil- 

 itic material. They have also found that the organism can pass 

 through the placenta of the rabbit and infect the foetus. 



The experimental production of the disease has supplied us 

 with some further facts regarding the nature of the virus. It 

 has been shown repeatedly that the passage of fluid contain- 

 ing the virus through a Berkefeld filter deprives it completely 

 of its infectivity; in other words, it does not belong to the 

 the ultra-microscopic group of organisms. The virus is also 

 readily destroyed by heat, a temperature of 51 C. being 

 fatal. With regard to the production of immunity, very little 

 of a satisfactory nature has so far been established. It has been 

 found that the virus from a macaque monkey produces a less 

 severe disease in the chimpanzee than the virus from the human 

 subject, inasmuch as secondary lesions do not follow ; the virus 

 would thus appear to have undergone a certain amount of 

 attenuation in the tissues of that monkey. The effects of inject- 

 ing emulsions of tertiary lesions or of serum from syphilitic 

 patients, at the time of inoculation with the virus, appear to be 

 nil ; so also the employment of the virus rendered inactive by 

 heating has apparently no influence in acting as a vaccine. 

 There is some evidence that the serum from a patient suffering 

 from the disease when mixed with the virus before inoculation 

 modifies the disease to a certain extent, but further evidence on 

 this point is necessary. 



Luetin. Noguchi has prepared an extract from pure cultures 

 of the spirochaete pallida, which he calls luetin, and he finds 



