2I 5 
containing caustic soda remained alive several days. It was 
concluded from tnis that none of the above chemicals could be used 
to advantage in killing gross vegetable matter such as grasses, and 
none were of special value as larvacides. 
An artificial pool as above was flooded with a 0125 per cent, 
solution of sodium arsenite. All but three or four of the stalks of 
grass were killed and overgrown with mould, the wilting effect 
becoming apparent in forty-eight hours. After nine days, when the 
grass was quite dead, several Culicine larvae were introduced into 
the pool and were killed after one hour’s exposure. The pool was 
twice flushed out to rid it of arsenic salt, but the grass showed no 
further signs of life at the end of thirty-five days. It was concluded 
from this that a (V125 per cent, solution is a valuable agent in 
destroying gross vegetable forms such as grass, and the resulting 
water in the pool remained effective as a larvacide. 
The common, green, filamentous algae, Spirogyra and Culicine 
larvae were introduced into small glass jars, containing various high 
dilutions of copper sulphate and sodium arsenite. The results of 
two series of experiments showed that copper sulphate in dilutions 
up to 1 part in 500,000 is inimical to the growth of this alga. They 
become greyish-green in colour, shrunken and lose their fresh and 
crisp appearance. As a larvacide, however, copper sulphate is not 
destructive in dilutions higher than 1 in 50,000 parts. Sodium 
arsenite, on the contrary, seems to stimulate the growth of these 
algae in all dilutions between 1 in 2,500 and 1 in 25,000,000, 
the algae remaining green and vigorous. As a larvacide, Culicine 
larvae were destroyed in sodium arsenite dilutions up to 1 in 100,000. 
The larvacidal powers of sodium arsenite solutions in contact 
with green algae seem to vary within wide limits, depending 
probably upon the power of the algae to take the arsenic salt out of 
solution into its own protoplasm, thus rendering the surrounding 
solution less larvacidal. It is concluded from this that coppei 
sulphate is more efficient than sodium arsenite as an algacide in high 
dilutions, but the arsenic salt is a better larvacidal agent. These 
results are in keeping with our pharmacological knowledge of the 
effect of copper and arsenic salts in high dilutions on animal and 
vegetable protoplasm. It would seem, then, that when grass and 
algae in pools, without outlets, are to be destroyed, sodium arsenite 
0 
