506 INFECTION AND RESISTANCE 



The most extensive studies in this respect are those of Neisser 142 

 and his associates in the Javan expedition. Briefly stated, Neisser 

 reinoculated 135 animals 165 times with negative result on the second 

 and subsequent inoculations. The second inoculations were made at 

 periods ranging from 21 days to two years after the first. In but 27 

 animals did the reinoculation show positive results, and in ten of 

 these cases only does Neisser recognize the experiments as valid. 

 Although these ten positive reinoculations, it is true, add an element 

 of irregularity to the series, they constitute but 6.8 per cent, of the 

 entire number, a proportion which in no way invalidates the experi- 

 ments when we consider that the work was done entirely on the 

 lower monkeys, animals that are far less susceptible to syphilis than 

 are human beings and in many of which, therefore, systemic dis- 

 tribution of the virus (a generalization apparently necessary for the 

 development of resistance) may not have taken place. Neisser's 

 conclusions, therefore, that monkeys, like human beings, are not 

 reinoculable while suffering from systemic syphilis, seem entirely 

 justified. 



His work, as well as that of Finger and Landsteiner, and of 

 Kraus and Volk 143 on lower monkeys, has shown that resistance 

 does not develop until the twelfth to the twentieth or twenty-first day 

 after the first inoculation; that is, again as in man, when the virus 

 has become generally distributed. Finger and Landsteiner, further- 

 more, noticed that reinoculation-products, obtained by reinfection 

 during the first incubation period, that is, before the development of 

 the primary lesion, were less severe and developed in a shorter time 

 than did the first lesion. This phenomenon which would tend to 

 mark another analogy to the conditions prevailing in human beings, 

 was not observed in the experiments of Neisser and of Kraus and 

 Volk. However, like the similar observation in human beings, it 

 seems to indicate the gradual acquisition of resistance as the virus 

 begins to exert its influence upon the tissues. 



Again, with monkeys as in man, the question arises whether the 

 resistance so unquestionably proven is a condition merely coexistent 

 with active disease, or whether it may be interpreted as a true im- 

 munity which persists after the microorganisms have been com- 

 pletely removed. The most directly pertinent experiments are those 

 of ^eisser. Neisser reinoculated monkeys at periods ranging from 

 27 to 645 days after the first infection. After waiting a time suffi- 

 ciently long to insure the negative result of the reinoculation, he used 

 organ-substance from these animals to inoculate other monkeys. In 

 22 experiments of this kind he obtained positive results showing 

 that the organs of the apparently immune animals still harbored 



142 Neisser. Beitr. z. Pathol u. Ther. d. Syphilis, Springer, Berlin, 1911. 



143 Kraus and Volk. Wien. klin. Wchnschr., 1906, No. 21, Ref. IX. Kon- 

 gress d. Dermatol. GselL in Bern. 



