276 
The strains of T. brucei employed killed rats in from five to seven 
days after inoculation. In the later experiments a particularly 
virulent strain was used which killed rats in from three to four days. 
This strain was obtained from a rat in which trypanosomes had 
reappeared after treatment by atoxyl. A similar result was obtained 
in four out of eight observations; more work is being done on this 
point. 
In all cases the rule laid down by Thomas and Breinl 1 was followed 
that the experimental treatment of animals infected with trypano¬ 
somiasis must not be undertaken unless the disease is well advanced— 
that is, unless the parasites are constantly present and the animal 
shows obvious signs of illness (loss of weight, &c.). -The poisonous 
dose of each drug, for the animals employed, was always ascertained 
as a preliminary step to experiment. The largest possible therapeutic 
dose was employed in every instance. The drugs were given 
subcutaneously in sterile solutions. 
Atoxyl, unless it was otherwise stated, was given in a 5 per cent, 
solution in sterile water. It was found necessary to use only fresh 
solutions, since atoxyl in solutions deteriorates rapidly. 3 
W hen experiments were first commenced, the solutions of atoxyl 
were kept for some little time.* It was noticed that their toxic effect 
on animals infected with T. brucei was evidently great. Out of 121 
rats, 40 died within 24 hours ; out of 58 rats at a similar stage of 
infection treated with freshly made solutions of atoxyl only 10 died. 
This increased toxicity on standing was confirmed by observations on 
a solution of 5 per cent, atoxyl in water which had been kept exposed 
to light for seven months. Rats inoculated with -5 c.cin. of this solution 
died within four hours. It is interesting to note that a similar solution 
of atoxyl kept for the same length of time in a dark-coloured bottle 
in a cupboard was not nearly so toxic. 
T or purposes of comparison it is well to state here that as a general 
rule T. brucei reappeared in the circulation of rats, treated by atoxyl 
alone, in from 16 to 25 days after the interruption of the treatment. 
ut of 113 rats treated by atoxyl in the same manner as was employed 
in our mercury' experiments (see below) only three are still alive (at 
1 26, 92 and 74 d ays after the cessation of treatment). In every case 
atoxy/wShad 8 stSd t0 " C eff ® Ct of aqUCOUS so,utionS ° f 
