Our results confirm the observation that Hetrazan does not possess activity against the adult worms. Although the lethal action of the drug against the microfilarias has been well demonstrated (10), most of our patients have shown a recurrence of the microfilarias after variable periods of negative biopsies extending up to 8 months, although in these cases the microfilarias were fewer in number than before starting the treatment. At times these recurrences could be explained by the presence of nodules containing living worms, but various patients (No. 2, 4, 9, 10, 12 and 15) did not show any nodules and still gave some positive biopsies. It is quite possible that adult worms were present that escaped detection and therefore extirpation. Also we may include the possibility that a certain proportion of the microfilarias may escape the action of the Hetrazan, harbored in some internal organ of the host.
Concerning the possibility of using Hetrazan prophylactically in endemic zones, it appears that only partial results can be obtained since the disappearance of the microfilarias does not occur in all the treated patients. It would be necessary to make studies on the density of microfilarias needed to insure infection of the simulid vectors. It seems evident that to obtain a permanent modification in the epidemiology of the disease it is indispensable to bring action against the vectors themselves with the object of decreasing their numbers. However, the administration of the drug to individual patients appears justified in view of the favorable clinical response obtained in most of the cases.