724 THE SPIROCILETE OF SYPHILIS 



Experiments on immunization. 



It is a general rule that an individual with a chancre cannot be re-infected, 

 but the rule is not without exceptions even in the case of the human subject 

 (Queyrat). In monkeys, a second inoculation 10 days after the chancre has 

 appeared may give rise to a second chancre (Roux and MetchnikofE). 



Individual human subjects exhibit considerable variation in their suscepti- 

 bility to syphilis and a similar variation is noticeable in the lower animals. 

 Young monkeys are much less susceptible than adults or old monkeys, and 

 among some species while the adults are easily infected the young animals 

 are immune (Roux and Metchnikoff). 



It would seem that the virus of syphilis can, in certain cases, become 

 attenuated by passage through the lower monkeys and that it then gives 

 rise in the higher apes and perhaps in man to a minimal local lesion which 

 is not followed by secondary manifestations and which moreover immunizes 

 the inoculated individual against a second inoculation. Unfortunately, the 

 results upon which this conclusion is based are very inconstant as will be seen 

 from the accounts of a few typical experiments which follow, and the method 

 cannot be regarded as a sure means of attenuating the virus. 



Metchnikoff and Roux inoculated a chimpanzee with a virus from a bonnet 

 monkey (M. sinicus}. Small insignificant chancres appeared but no secondary 

 lesions and the chimpanzee was immune to a subsequent inoculation with a 

 human virus. The experiment was repeated several times but the above 

 result was never again obtained. 



Finger and Landsteiner obtained a virus which after passing through six 

 baboons (C. hamadryas] in succession set up in a seventh an insignificant 

 lesion which lasted only a short time. In another experiment the virus 

 showed no attenuation after twelve passages. 



Roux and MetchnikofE passed a virus from a chimpanzee through a number 

 of M. rhesus. As it passed from rhesus to rhesus the primary sore became 

 more and more benign and appeared earlier, the incubation period at the 

 same time falling from 197 days. After eleven such passages, the virus was 

 very attenuated for rhesus monkeys and harmless to the chimpanzee. 



Roux and Metchnikoif inoculated a man 79 years of age, and who was not 

 known ever to have had syphilis, on the fore-arm with an human virus which 

 had been passed through five monkeys, a baboon, two chimpanzees, and two 

 bonnet monkeys (M. sinicus}. Twelve days after the inoculation two insignifi- 

 cant papules appeared which lasted only a few weeks and were unaccompanied 

 by any other lesion. The controls (a chimpanzee and a bonnet monkey) 

 developed typical chancres after incubation periods of 23 and 31 days 

 respectively. 



Sub-cutaneous inoculation of anthropoid apes with syphilitic material does 

 not produce the disease. This being so it might be thought that sub-cutaneous 

 inoculation would have an immunizing effect but by experiment this is 

 found not to be the case ; animals inoculated sub-cutaneously are just as 

 easily infected by scarification as the controls (Metchnikoff, Roux and 

 Neisser). 



The syphilitic virus after being heated to 51 C. has no immunizing action 

 when inoculated into susceptible animals. 



Serum therapy. Up till now all attempts to obtain an antisyphilitic serum 

 have failed. Roux and Metchnikoff attempted the preparation of a serum 

 by inoculating macacus monkeys and baboons which had recovered from 

 a primary sore with large quantities of a virus of human origin. The serum 

 of these monkeys sometimes neutralizes the human virus in vitro : a mixture 



