The following conclusions are drawn from the results of the 40 experiments described above: 1) From the 2nd to the 8th month there is a great resistance to super-infection. a) Such resistance seems to be independent of the presence of cutaneous lesions and occurred even in cases with only the initial lesion. b) Within this period, resistance disappears with treatment: patients treated and reinoculated acquire yaws in the normal time. This fact suggests that this resistance is conditioned by the presence of an active or latent infection, being not a true immunity (an immunity in its classical conception). c) When homovirus is used, resistance lasted about one year of the disease. 2) From the 10th month to the 4th year of the disease, there is a partial resistance, which manifests itself by two modes, according to the nature of the atypic lesion obtained at the spot of inoculation: a frustrated papulo-erythematous lesion and a pianide similar to that of the natural infection, which may be micropapulo-erythematous or papulo-erythemato-escamous and remains localised without metastatic manifestations at least during the 4th months in which it was observed. a) This state of partial resistance also seems independent of the presence of evident yaws lesions. b0 This state is not modified by treatment. The patients treated during this phase of the disease react to the inoculations in a similar way, though without showing any clinical symptoms and with a negative Wasserman reaction. Doubtless the "frustrated lesions" as well as the "pianides" obtained by the inoculation of the patients as referred above, may he considered as resulting of a certain degree of acquired immunity, much stronger in the case of the "frustrated lesions". 3) After the fifth year of the disease superinoculation reveals a greater sensitiveness of the infected organism. A precocious papulo-erythematoulcerous, decidely necrotic and destructive lesion, develops at the spot of inoculation. An exacerbation of the lesions of the patient occurs at the same time, and is accompanied by great swelling of the nodes. The lesion obtained in one case remained in situ for 18 months without producing generalised manifestations. a) Treatment does not modify this state. Patients treated (and partially or totally cured) react in the same way to reinoculation within this period of the disease. Amongst the 13 cases infected for more than five years, only one (nr. 40) did not develop "ulcero-necrotic lesion". He was also the only case who never presented gummatous and destructive lesions. On the other hand, two patients presenting these lesions, but infected for less tham 3 years, also did not develop 'ulcero-necrotic lesion" when superinoculated. It is interesting to note that this lesion contains treponemes, thoughonly a few, and that its evolution may lead to gummatous ulcerative processeswhich characterize the tertiary period of the disease, and with a similar histopathology. 4) From the epidemiological point of view, it is advisable to await the end of the secondary period of the disease, that is the generalised phase, before treating patients at hospitals, since they will become reinfected if they return to the focus. From the therapeutic prophylactic point of view in the focus, the primary and secondary lesions must be eliminated rapidly as they are most contagious as they contain the greatest number of germs. 5) In framboesia tropica there is a true immunity and not a simple resistance to superinoculation owing to a low infection or a latent one. The patients treated at a certain period of the disease and cured both clinically and serologically show partial resistance to reinoculation, and react in a fashion similar to of that of other untreated patients in the same period. 6) Immunity, in framboesia tropica, takes the form of resistance to superinoculation, or of a modification of the initial yaws lesion, or again as a resistance to the generalisation of the disease. 7) The results of these experiments suggest that the different cutaneous manifestations of the disease are more or less conditioned by the state of immunity of the infected organism. 8) In framboesia tropica, the different degree of immunity are related to the age of infection. They are reached more or less rapidly, according to the individual characteristic of the infected organism, as well as to the virulence of treponeme, just as it happens with the secondary and tertiary periods of the disease.