POISONOUS PLANTS 387 
the course in less than an hour. Within two minutes after the application on 
any part of the stream all mosquito larve there were dead. 
“T remained several hours afterwards, so as to be able to work alone, dipped 
and looked carefully on knees and hands all along that stream, but not one live 
larva was found, where hundreds could be taken in a single dip before. 
“ A few hours after the application the water course was again quite clear and 
could be used for drinking and washing as before. 
“The vegetation did not appear to have suffered in any way, though that 
might take longer to show. Most of the other water insects were dead, but a 
considerable number of water beetles, Hemiptera and dragon-fly larve withstood 
the treatment, and I have no doubt but that the percentage of the larvicide 
solution can be so regulated that it would kill all the mosquitoes and not the 
tougher predaceous insects. 
“ There were no fish in the stream, so I can not say, from personal observa- 
tion, how it would affect them, but Mr. Trask says they can endure considerable 
of the larvicide without dying.” 
DESTRUCTION OF LARVE BY SENSITIZATION TO LIGHT. 
Dr. Gunni Busck, of Copenhagen, has recently carried out novel experiments 
in mosquito destruction : 
“T have this fall tried to solve the question of killing mosquito larve by an 
entirely different method, on the supposition that it might be possible, through 
solutions of suitable coloring matter (Erytrosin, Rose Bengal, etc.), to sensitize 
mosquito larva: so that they would be killed by the sunlight or mere daylight, 
to which they are directly exposed under natural conditions, when they assume 
their normal position for respiration at the surface of the water. 
“Tt was shown by my experiments that it really is possible to thus sensitize 
mosquito larve and that they die in thin solutions of the above mentioned 
colors, if they are exposed to light, even if only diffused daylight, while they 
remain alive, pupate and develop to adults in these same solutions, if they are 
kept in darkness. 
“Tt was however necessary to use more concentrated solutions of the colors 
than I had anticipated, and as these colors moreover are rather expensive, the 
method can at present in no wise compete with the oil methods. The experi- 
ments will be continued and their scope widened this coming season.” 
POISONOUS PLANTS. 
Decoctions and emulsions of an African leguminous plant, Derris uliginosa, 
have been recommended for larvicidal use, and experiments conducted by Bal- 
four at the Wellcome Research Laboratories at Khartoum show that it has con- 
siderable potency. It also kills fish, different species of Derris being well known 
for this quality, so that even in regions where these plants are native they have 
only a limited use as insecticides. 
Recently Daniels (Tropical Medicine and Hygiene, Part 1, 1909, pp. 77-78, 
120) has advocated the use of the “tuba root,” also belonging to the genus 
Derris, which is used in the East Indies to poison fish, to destroy mosquito larvee. 
The commonly employed species is Derris elliptica. Other plants are employed 
in other parts of the world to stupefy fish and some of these might prove to be 
effective against mosquito larve. Daniels says of Derris: 
“The roots are crushed and thrown into the water, and the milky fluid from 
the fresh roots, even in minute quantities, and much diluted, will destroy the 
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