1907.] Experimenta I 7 reatment of Trypanoso n i iasis in Rats. 509 



trypanosomes from the blood, even when in very large numbers, but there 

 remain behind certain forms of the parasites which can resist it, and which 

 after an interval can reproduce the general infection with the indifferent forms. 

 These recurrences can take place, in our experience, up to as many as seven 

 times. The resistant forms appear to be located in the intermediate 

 periods in the bone-marrow, but there is some doubt about this yet, as in 

 some cases we have failed to produce an infection, even with a quantity of the 

 marrow. It is probable also that some of these resistant forms may be found 

 in the glands, and observations are being carried out on these points. But 

 when an infection is produced from the marrow of these atoxyl-treated rats, 

 the incubation period is very much prolonged, and it may be as long as 

 nine days before trypanosomes can be found in the blood of the inoculated 

 animals. 



Atoxyl appears to act not by virtue of the arsenic in it alone, but its effects 

 are probably due to this in combination with some other of its constituents, 

 as its action is much more rapid and complete than that of any other of the 

 simpler arsenic compounds which we have tried. 



The following Tables I and II give the results of treatment with atoxyl 

 and succinimide of mercury : this latter has been given either with the atoxyl 

 or immediately after it, the best method being, we think, to give two or three 

 doses of atoxyl and to give a dose of succinimide of mercury at the same time 

 as the second and third doses, with perhaps one after. Some of our rats have 

 had too much, and we are now giving less with better effect. The succinimide 

 has the great advantage of being unirritating to the tissues, and it will mix 

 with atoxyl without precipitation, and without, at any rate, interfering with the 

 action of the latter. 



