722 THE SPIROCELETE OF SYPHILIS 



Metchnikoff, who in 1903 demonstrated that these animals were susceptible 

 to the virus of syphilis. 



I. Chimpanzee. The chimpanzee is the most suitable animal for the 

 purpose of studying syphilis experimentally. Compared with man this 

 species may be regarded as equally susceptible to syphilis. Inoculation 

 under the conditions described below is certain to result in infection (Roux 

 and Metchnikoff). 



The virus is best obtained from a chancre or secondary lesion and should 

 be inoculated into superficial scratches made on any part of the body, but 

 preferably on the superciliary ridges, upper eyelids or genital mucous mem- 

 brane. Infection cannot be produced by inoculation beneath the skin, into 

 the peritoneal cavity or into the blood vessels. 



The incubation period averages 31 days (22-35). Exceptionally it may be 

 reduced to 15 or prolonged to 49 days. 



Chancre. After a period of incubation has elapsed, small, rose-coloured, 

 hardly visible pimples make their appearance at the site of inoculation. Two 

 or three days later the lesion is redder and a small scale forms on the surface 

 followed by ulceration and induration of the subjacent tissues, reproducing 

 exactly the appearance of the chancre as seen in man. The corresponding 

 glands become enlarged and indurated. 



Secondary manifestations. Secondary lesions have been observed in 66 per 

 cent, of chimpanzees inoculated and are recognizable about a month after 

 the appearance of the chancre. 



The rash is very difficult to detect because chimpanzees suffer naturally 

 from rashes on the skin which may very easily be mistaken for a typical rose 

 rash (Roux and Metchnikoif). On the other hand, papules and mucous 

 patches are seen and inoculation from these into another chimpanzee results 

 in infection of the latter. During the secondary stage, Roux and Metchnikoff 

 have observed attacks of paraplegia coming on a few weeks after the appear- 

 ance of the chancre but soon passing off. The spleen is frequently enlarged. 



One of the chimpanzees inoculated by Roux and Metchnikoff suffered from 

 a malignant form of syphilis and died about 10 months after infection. 



Tertiary manifestations. Tertiary lesions have not up to the present time 

 been observed in chimpanzees. 



II. Orang-outang. Inoculation of syphilitic material into an orang-outang 

 invariably produces a chancre (Neisser, Roux and Metchnikoff). 



The incubation period is shorter than in the chimpanzee and averages 

 24 days. 



The chancre is not so distinct as in the chimpanzee. Secondary mani- 

 festations apparently never develop. 



HI. Gibbon. The results of the inoculation of the gibbon are almost the 

 same as in the orang-outang (Metchnikoff and Neisser). Secondary mani- 

 festations are uncommon. Neisser has noticed a papular eruption covering 

 the face, palms of hands, abdomen, buttocks and mucous membranes. 



As has been pointed out already the higher apes may be infected by scratching 

 infective material taken from a primary or secondary lesion into the skin of any 

 part of the body. When material from tertiary lesions was used five only out of 

 seventeen experiments were successful (Neisser, Sieber and Schacht). Hoffmann 

 inoculated four animals with the blood of a syphilitic man (taken 40 days and 6 

 months after infection) while it was still warm and before it had coagulated. Two 

 of the animals developed syphilis. The same observer succeeded in infecting a 

 monkey with mucus from the nose of a diseased person. 



Investigation shows that the virus of syphilis diffuses very rapidly through the 

 tissues. Excision of the site of inoculation 8 hours after infection does not prevent 

 the development of a chancre. During the incubation period the bone- marrow and 



