YAWS AND SYPHILIS 285 
S. pertenuis and S. pallida (which are identical morphologically) and in the 
inoculation of animals with the two viruses, may very well apply only to dif- 
ferences in individual strains of these organisms, since different strains give 
very different results. Much of the careful work of Nichols,! Brown and 
Pierce ? and Kolle * and the observations of Chesney,‘ and others have empha- 
sized this fact. Also the different pathological lesions obtained in rabbits by 
Pierce and Brown by the inoculation of yaws and syphilis virus might be ex- 
plained by differences in virulence of the two strains or as protean manifesta- 
tions of the same affection. 
The earlier experiments performed by Neisser, Baermann, and Halberstad- 
ter,° and Castellani ° seemed to show that in three instances monkeys previously 
inoculated with syphilis could subsequently be inoculated with yaws, and vice 
versa, that four monkeys inoculated with yaws could subsequently be infected 
with syphilis. But the work of Levaditi and Nattan-Larrier’ showed that 
five monkeys which were first inoculated with syphilis were subsequently im- 
mune to yaws. The experiments, however, are not sufficient in number from 
which to draw definite conclusions. In connection with them, Schobl * has 
shown that monkeys infected with yaws do not develop a high degree of immu- 
nity to the infection in less than seven months’ time. Hence the positive results 
on reinoculation before this period would not be conclusive. Moreover, Schobl 
after an extensive serological study of yaws and syphilis during several years, 
in his most recent publication with Miyao on the subject, concludes that Philip- 
pine monkeys that have gone through yaws infection produced by the Kadangan 
strain and were found to be highly immune to yaws, by repeated inocula- 
tions with homologous strains were also found to be immune to cutaneous inocu- 
lation with the Nichols strain of syphilis. He has therefore shown that a high 
degree of immunity to yaws protects against cutaneous infection with syphilis 
in Philippine monkeys. 
With reference to experiments upon rabbits, the early experiments of Nichols ® 
suggested that infection with yaws would not confer upon these animals pro- 
tection against syphilis, but in these experiments the interval between inocu- 
lations was also comparatively short. More recently, however, Nichols! has 
brought forth evidence to show that rabbits that have been infected with yaws 
and have carried their infection for a comparatively long period of time, 91 to 
376 days, may, in approximately fifty per cent of the cases, whether treated or 
not, be refractory to a subsequent inoculation with a strain of Treponema 
pallidum which is highly virulent for the rabbit. 
1 Nichols: Amer. Jour. Trop. Med. (1925), V, 429. 
2 Brown and Pierce: Jour. Exper. Med. (1925), XLI, 678. 
3 Kolle: Deutsche Med. Woch. (1926), LII, 11. 
4 Chesney: Medicine (1926), V, 463. 
5 Neisser, Baermann, and Halberstadter: Munich. Med. Woch. (1906), LIII, 1337. Arb. a. d. kais. 
Gesundheitsamte (1907), p. 48. 
6 Castellani: Jour. Hyg. (1907), VII, 558. 
7 Levaditi and Nattan-Larrier: Ann. Inst. Pasteur (1908), XXVIII, 260. 
8 Schébl and Miyao: Philippine Jour. Sci. (1929), XL, 91. 
9 Nichols: Jour. Exp. Med. (1911), XIV, 196. 
