221 
NOTES ON THE EFFECTS OF THERA¬ 
PEUTIC AGENTS ON TRYPANOSOMES 
IN RESPECT TO {a) ACQUIRED RESIS¬ 
TANCE OF THE PARASITES TO THE 
DRUG, AND {b) CHANGES IN VIRULENCE 
OF THE STRAINS AFTER ESCAPE FROM 
THE DRUG 
BY 
BENJAMIN MOORE, M.A., D.Sc. (R.U.I.) 
JOHNSTON PROKESSOR OF BIO-C HK.M tSTKY 
MAXIMILIAN NIERENSTEIN, Ph.D. (Berne) 
INTERNATIONAL RESEARCH FELLOW 
AND 
JOHN LANCELOT TODD. B.A., M.D. (McGill), M.R.C.S. 
PftOFF^SOR OF PARASITIC PROTOZOOLOGY, McGlI.L UNIVERSITY, MONTREAL 
the Departments of Bio-Chcmisiry and of Tropical Medicine, 
University of Liverpool) 
{Received for publication ii May, 1908) 
A. DEVELOPMENT OF DRUG-PROOF STRAINS . 
It is a well-established fact in the therapeutics of trypanosomiasis 
that, with each fresh recurrence of the parasites in any case, these 
become more resistant to the drug employed, and more difficult to 
tifive out of the peripheral circulation. 
This is not only the fact in any given case, but also as was first 
shown by Ehrlich* in the case of rats treated by atoxyl; the parasite 
'tself, apart from the individual host, becomes resistant to the drug, 
when passed to fresh animals of the same species, reaches finally 
^ condition in which it is resistant or ‘fast’ to the particular drug. 
This condition Ehrlich expressed by the term ‘ Atoxyl-fest ’ in the 
of trypanosomes which had become refractory to the action of 
atoxyl 
‘Berl. Klin. Wochensch., 
•Oo:, p. 33. 
