4 BULLETIN 1023, U. S. DEPARTMENT OF AGRICULTURE. 



of the discrepancies between the results of various observers (19), 

 (30) on the hedgehog. Different batches of frogs sometimes vary 

 in sensitivity toward strychnine. Neither the relation of this varia- 

 tion to the temperature and season nor the range between the con- 

 vulsive and lethal doses has been determined. 



The respective tolerance for any species of the adult homothermal 

 mammals thus far studied has not varied markedly, the data reported 

 in the literature by investigators who employed accurate methods 

 agreeing very closely. Hunt and Seidell (12) have shown that while 

 the tolerance of rats and mice to morphine varies with the dietary 

 conditions, the toxicity of strychnine remains constant. Judging 

 from the reliable data in the literature, no variation in the toxicity of 

 strychnine caused by either diet or season occurs in* other " warm- 

 blooded " animals. In fixing the lethal dose, however, it would be 

 advisable to perform many series of experiments, under suitable con- 

 ditions, to rule out individual dietary and environmental factors. . 



Another modification which has occurred in the course of evolu- 

 tion is a tendency for a decrease in the number of spasms preceding 

 death. Lower vertebrates, certain low mammals (24) , and some very 

 immature higher mammals (2), (5), (6), (15), (25) have multiple 

 spasms preceding death. In certain immature mammals of the 

 higher order a wide range between the convulsive and lethal doses 

 exists. Very young animals are comparatively resistant to asphyxia 

 and recover their ability to breathe more easily than mature mem- 

 bers of the same species. On this account they can endure more suc- 

 cessfully a large number of convulsions. This explanation, however, 

 probably is not entirely adequate, for the reason that other character- 

 istics differentiate the immature from the mature mammals here 

 considered. 



The size of the effective dose changes with the age of the mam- 

 mals of certain species (25). At birth the mouse, rabbit, cat, and 

 dog possess a natal immunity against the fatal action of strych- 

 nine, in this respect resembling the lower forms of animal life. 

 Upon further development, however, this resistance is lost. After the 

 decline of this resistance in the mouse a post-natal immunity, which 

 reaches its limit about the time of sexual maturity, develops. The 

 guinea pig also develops such a post-natal immunity, but, owing 

 to its relatively mature state at birth, the decline of the natal im- 

 munity seen in other animals presumably is eclipsed by the period 

 in utero. The cat, dog, and rabbit apparently develop no post-natal 

 immunity, the adult lethal dose remaining at about the level to which 

 the natal resistance declines. 



Strychnine differs from many other poisons in that the body dis- 

 poses of it very rapidly. The fact that small amounts of strychnine 

 may appear in the urine for several days after its administration 



