BY H. G. CHAPMAN. 293 



To determine the minimal lethal dose for Hyla aurea, 108 

 experiments have been carried out. These have been conducted 

 at different periods of the year to render obvious the effect of the 

 winter and summer seasons. Series of experiments have also 

 been performed to exhibit any differences in resistance between 

 frogs fresh from their native swamps, and frogs from the 

 laboratory tank. 



In all cases the strychnine was dissolved as sulphate and 

 introduced into the dorsal tymph sac by a hypodermic needle. 

 The concentration of the solution of strychnine was adjusted to 

 allow the introduction of the poison in less than 1 c.c. of normal 

 salt solution. For most experiments a solution containing 5 mg. 

 of strychnine as sulphate in 1 c.c. fluid was employed. The 

 solution was measured in a pipette carefully graduated into 

 hundredths of a cubic centimetre. The amount for each dose 

 measured by the pipette was then sucked up by the needle and 

 injected. The experiments were conducted in series of six frogs 

 each. These were weighed to the nearest decigram and kept on 

 a board under large glass beakers during the experiment. 

 Moistened cotton wool was placed beneath the beaker. Each 

 twenty-four hours the whole was cleaned to avoid infection of 

 the frogs. The time at which the frogs were injected was noticed 

 and the period between the first spasm and the injection noted. 

 Frequent taps were given to the board on which the frogs were 

 placed to elicit convulsions. 



In the earlier series the frogs were not arranged in any order 

 from the point of view of their weight. Later it was thought to 

 be more advantageous to arrange the frogs in such an order that 

 the heaviest frog received the smallest dose per gm. of weight 

 and the lightest frog the greatest dose per gm. of weight. 

 Although the absolute weight of the frog had little or no 

 influence on the ultimate fate of the frog, it appeared that small 

 frogs became convulsed earlier than large frogs. 



Certain typical results are tabulated in Table i. in which the 

 weight of the frogs, the dose, and the behaviour are recorded. 



