CONCERNING THE EFFECTS OF "TUBA" FISH-POISON. 131 



does not seem to lose consciousness until the breathing is g'reatly 

 affected. Post mortem examination shows venous congestion of 

 the organs ; the heart is full of blood, but still capable of con- 

 tracting in response to stimuli. If the heart be examined soon 

 after the breathing has stopped, it is observed to be beating feebly, 

 and if relieved from the distension with blood, will beat for a long 

 time. 



From these observations it seems very probable that death is 

 due to asphyxia. 



Another series of experiments was done in which a small 

 quantity (1 cubic centimeter) of the extract was injected into the 

 stomach of the fish by means of a long narrow metal tube passed 

 down the oesophagus. 



The minimal lethal dose, in this manner of injection, is the 

 extract obtained from 1/200 gm. of the root. The extract actually 

 injected is 1 c. c. 1 in 200 solution. The symptoms of poisoning 

 are exactly the same as those described above. The poison is rapid- 

 ly absorbed by the stomach, the fish becoming affected two minutes 

 after the injection. Wray (9) points out that "tubaine" is in- 

 soluble and that he has seen a fish eat a quantity without ill effects. 

 I have not used the isolated substance " tubaine/' but the milky 

 extract is certainly rapidly fatal when administered in this way. 

 The extract from 1/25 gm. of the root kills fish in twelve minutes, 

 from 1/200 gm. in one hour. 



I have not experimented with fish larger than 50 gm. Un- 

 doubtly larger fish would require larger doses to kill them. 



Effects on Tadpoles. Tadpoles of the common Singapore 

 toad, Bufo melanostictus, were immersed in solutions of various 

 concentrations. The symptoms of poisoning closely resemble those 

 described for fish, but stronger solutions are required. Solutions 

 weaker than 1 in 12,000 do not kill tadpoles. A solution 1 in 

 12,000 kills in forty three minutes and a solution of 1 in 4,500 in 

 twenty minutes. These solutions kill fish in half these times 

 respectively. 



Effects on Mosquitce Lauv^e. Stegomyia larva? were em- 

 ployed. Solutions weaker than 1 in 10,000 are not fatal, nor do 

 they prevent the larvae developing. A solution 1 in 10,000 takes 

 at least two days to kill larvae ; 1 in 5,000 kills them in about two 

 da^ys; 1 in 1,000 in one day, 1 in 500 in three hours, 1 in 10 in 

 one hour. Therefore much stronger solutions and much longer 

 periods of action are required to kill mosquitce larva? than to kill 

 fish or tadpoles. 



Effects ox Toads. The common toad, Bufo melanostictus, 

 was employed. The poison was administered either by subcu- 

 taneous injection or by injection into the stomach of one cubic 

 centimeter of the fluid extract. The minimal lethal dose by the 



R. A. Soc, No. 73, 1916. 



