396 THE HUMAN SPECIES 



John Siegel of Berlin, who regards syphilis as closely allied to 

 the acute exanthemata, found a microscopic protozoon belong- 

 ing to the flagellates which he considered as the exciting 

 cause ; he traced its development from the early stages by 

 means of a special culture medium of the blood of syphilitic men 

 and rabbits ; and finally he produced iritis and other syphilitic 

 lesions in other animals, although he admitted that all previous 

 cultural experiments had failed. 1 



Metchnikoff and others have now established the transmissi- 

 bility of syphilis to apes by means of dermal inoculations, and 

 a blood reaction for syphilis has been worked out by Wasser- 

 man. These results may prove of great importance for the 

 prophylaxis of the disease in man. 



The biology of the acute exanthemata is still very obscure, 

 and will require much more laborious investigation for their 

 elucidation. According to references in the earlier literature 

 collected by M. Schmidt, monkeys as well as man can be 

 primarily infected with small-pox. Thus, in ah epidemic of 

 small-pox in Trinidad (1858), the wild monkeys were attacked, 

 and in the year 1841 a traveller in a forest on the way to 

 David (Chiriqui) saw monkeys suffering from small-pox which 

 four or five days later broke out in David. Except for these 

 isolated reports, small-pox has always been regarded as a purely 

 human disease. Since, however, it has been recently shown that 

 small-pox can indubitably be conveyed to calves, and vaccine 

 pustules be produced in man by inoculation from this material, 

 the identity of cow-pox and small-pox seems fully established. 



The remaining acute exanthemata, namely, measles, rubeola, 

 chicken-pox and typhus fever, are absolutely specific for man, 

 all attempts at infecting animals having produced negative 

 results. Human typhus is not identical with the petechial fever 

 in horses and cattle. For none of these four very elusive 

 diseases has any causal organism been found, although certain 

 protozoon-like forms have been observed in small-pox, and 

 their connection with the disease more or less established. 



1 Apparently the Spirochaete pallida (a species of protozoon) discovered by 

 Schaudinn and described as the specific cause of syphilis is only a modified form 

 of the round protozoon described by Siegel. 



Siegel, J., " Untersuch. iiber die Aetiologie der Pocken, und der Syphilis," 

 Med. Klinik, 1905, No. 18, p. 446. 



