A. Bacot and (t. Talbot 
*229 
(3) No. 22 was impossible to apply satisfactorily, even by the use of 
heat or water; most of it flaked off, but left a strong odour behind. Put up in 
altered form as 22 a it still left much to be desired as regards its spreading 
properties, after the lapse of an hour or more becoming too dry to adhere 
properly to the skin. 
The preliminary trials indicated that some of the preparations showed 
the maximum degree of efficiency in relation to the conditions of the test, 
whereas others only afforded a partial degree of protection. 
Between the first census of bites and a second one carried out on June 
20th, when 39 bit in cage A, and 59 in cage B, there was apparently a con¬ 
siderable reduction in the biting population of the cages. It is not easy to 
estimate the amount of this reduction, or exactly when it occurred, owing to 
the early method of allowing no interval between the insertion of the treated 
and the control arm—which confused the issue. The reduction must however 
be attributed to the heavy death rate occasioned by drowning and drought. 
Subsequently, after the cages had been covered in by waterproof paper, and 
leaves had been placed in the water receptacles, the death rate was minimised 
and the population increased, any fluctuations being due either to the intro¬ 
duction of recently reared adults or to deaths owing to the natural completion 
of the life cycle. 
The early tests were repeated after the population had increased, so that 
the trials of the preparations were brought into conformity with the others. 
In Table I both tests will be found bracketed against the preparation. 
In a few tests (Preparations Nos. 10, 11, 15, 20, 21 and 22) the temperature 
altered during the period between test and control; in such cases both 
temperatures are recorded. 
IX. EXPERIMENTS, SERIES II. 
The Duration of the Period of Effectiveness. 
For the purpose of military use it is of special importance that the pro¬ 
tection afforded should cover as long a period as possible. A further series 
of trials was therefore arranged in order to determine for what period pro¬ 
tection would be afforded. 
Preliminary trials in connection with this series showed that it was useless 
to expect protection to be conferred for a longer period than a few hours at 
most, the better preparations affording practically no protection after the 
lapse of 16 and 8 hours respectively. The period of trial was therefore reduced 
first to 5, then to 3, and finally to 2 hours. 
The efficient culicifuges, comprising Nos. 1, 2 a, 5, 9 a, 9 b, 10, 11, 15 a, 
21 and 22 a were alone included in this series of trials. The results obtained 
are given in Table II. 
