218 MALAY POISONS AND CHARM CUBES 



Six species 6f derris were tested, but only two of them 

 (D. elliptica and 1). uliginosa) were considered useful for 

 insecticidal purposes. It kills some insects easily and 

 others with difficulty, but it usually acts slowly and 

 seems to kill by motor paralysis. It proved to be 

 efficient against most of the aphides in the form of a 

 spray. The green apple aphis (Aphis pomi, De Greer) 

 is destroyed at the rate of 1 pound of derris to 

 200 gallons of water under field conditions. Dr. H. E. 

 Durham found (190B) that the most sensitive animals 

 are perhaps the Daphnid Crustacea. Tadpoles and 

 water-snails are also easily killed. Caterpillars are 

 easily poisoned ; specially sensitive is the gooseberry 

 saw-fly (Nematus ribesii), but Durham found that it 

 had no effect as a contact poison on the black bean 

 aphis (A. rumicis) and the woolly aphis of the apple 

 (E. lanigera). Trial on fi'ogs' hearts showed that the 

 vagus was paralysed, so that stimulation of the nerve 

 failed to cause the normal vagus inliibition (Eef. 7). 



Campbell found that an extract from 30 grains (2gms.) 

 of the root was sufficient to kill a large monkey in about 

 forty nunutes. He observed that it usually stimulates 

 the respiratory centre before depressing it and that it 

 acts as a vaso-dilator. " The poison acts upon the 

 respiratory nervous centre in the medulla and not on 

 the vagal endings in the lungs, because the same results 

 are obtained if the vagi are cut. Also if the poison is 

 injected into the carotid artery, the respiration is 

 affected in a few seconds." He found that post- 

 mortem examinations only showed venous congestion of 

 the organs. 



In 1902 Durham (Ref. 7) commenced a series of 

 experiments with tuba as a larvicide in the Federated 

 Malay States. In England he found that Culex larvae 

 (Theobaldia annularis) were killed in 1 in 40,000 



