36 BULLETIN 800, U. S. DEPARTMENT OF AGRICULTURE. 



Steer 750, after a small feeding on August 22, received August 25 

 0.626 pound without effect, was poisoned on August 26 bj' an un- 

 determined quantity, and killed September 22 by 0.551 pound. 



In none of these cases is there any clear evidence that Asclepias 

 galioides should be considered a cumulative poison. Neither did the 

 fact that an animal had been poisoned once increase its suscepti- 

 bility to the effect of the poison. It is doubtful, too, whether we are 

 justified in thinking that any marked degree of tolerance is acquired 

 by repeated feeding. Sheep 478 was not affected June 19 by 0.165 

 pound, but after repeated doses, ranging from 0.11 to 0.147 pound, 

 was made ,sick on September 5 by 0.167 pound. Sheep 506 was 

 given repeated doses with small increases until it was killed on 

 September 20 by 0.184 pound, having shown symptoms on September 

 11 from 0.148 pound. This sheep, taken by itself, may possibly be 

 considered as having acquired some tolerance, yet the difference be- 

 tween the fatal dose, 0.182 pound, and the toxic dose September 11 of 

 0.148 pound, is not great, and in the case of Sheep 478 the difference 

 between 0.165 pound, which produced no results, and 0.167 pound, 

 which produced symptoms, is negligible. 



In the case of Steer 750 evidently no tolerance was acquired. 



The experience with Sheep 522 may be considered as conclusive evi- 

 dence that neither is the plant a cumulative poison, nor is any toler- 

 ance acquired by repeated feedings. 



SEASONAL VARIATIONS IN TOXICITY. 



The material from Hotchkiss, Colo., used in the experiments, con- 

 sisted of young plants in bud. That obtained from Paonia, Colo., 

 Rockville, Utah, and High Rolls, N. Mex., was in flower, while that 

 obtained from Grand Junction, Colo., and Palisades, Colo., was 

 in flower and fruit. The number of experiments was not sufficient 

 to show definitely whether there is a variation in toxicity at different 

 seasons or not, but so far as the work went the plant appears to be 

 uniformly toxic at all ages. 



No experiments were made with the plant cured and dried stand- 

 ing, but the numerous accounts of the loss of sheep when feeding 

 upon the plant in this condition make it reasonably certain that it 

 retains more or less of its toxicity. It follows that losses maj^ occur 

 at any time when the plant can be obtained and that hay containing 

 any considerable quantity is dangerous. 



RELATIVE TOXICITY OF LEAVES AND STEMS. 



In the experiments of 1918 the whole plant was used. Inasmuch 

 as it was desirable to know whether all parts of the plant were 

 equally toxic, a number of experiments of feeding leaves only and 

 stems only were made in 1919. 



