The results observed in different specimens allow us to draw some preliminary conclusions concerning the influence of treatment with dihydrostreptomycin and isonicotinic acid hydrazide on the anatomical chansges of tuberculous lesions. These conclusions may be summarized as follows:

Dihydrostreptomycin and isonicotinic acid hydrazide admimsistered ins large qunanities do not appear to bring about a complete reversal of specific changes. This was found to be true even when treatment was begun simultanseously with the inoculation.

In almost all of the cases treatment proved highly beneficial in respect to progression of the experimental lesions. In all treated animals the lesions were smaller than in the constrols and were more sharply demarcated. The drugs appeared to have the greatest influence on the development of the lymphatic lesions. In no instance was there histological evidence of cure or of the development of a productive or cicatricial reactions as the result of treatment.

A comparative study of specimens obtained before and after treatment showed that the main action of the drug is to inhibit the spontaneous progressive course of the process. There is little influence on its regressions.

A comparison between animals treated with dihydrostreptomycin and isonicotinic acid hydrazide in equivalent doses shows almost no difference between the effects obtained with the two drugs.