TRANSMISSION OF THE DISEASE TO ANIMALS 509 



lesion been observed. By re-inoculation from the lesions, the 

 disease may be transferred to other animals. The disease may 

 also be produced in baboons and macaques (macacyj sinicus is 

 one of the most susceptible), but these animals are less susceptible, 

 and secondary manifestations do not appear. The severity of the 

 affection amongst aj>es would in fact appear to be in proportion to 

 the nearness of the relationship of the animal to the human 

 subject. 



AJ <ho\vn tirst by Hansell, and more recently by Bertarelli, the 

 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 recently studied the stages in 

 detail, and find that the spirochaetes remain in the inoculated 

 material unchanged for a time ; then organisation occurs and 

 the spirocha3tes multiply, and later still there is a more rapid 

 multiplication and invasion by them of the tissues of the eye. 

 The period of incubation is thus not due to the organism passing 

 through some cycle of development, but simply to its requiring 

 certain conditions for multiplying which are not supplied for 

 s mil- time. 



The production of the disease, experimentally, has supplied 

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

 It has been shown repeatedly that the passage of fluid con- 

 taining the virus through a Berkefeld filter deprives it completely 

 of its infectivity. In other words, the virus does not belong to 

 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 



