TRACE ELEMENTS IN ANIMALS 129 



developed typical symptoms of alkali disease, namely, loss of 

 hair and disturbance of the growth of the hoof, and all died in 

 from 10 to 99 days. Post-mortem examination revealed lesions 

 of internal organs, particularly of the liver, while kidneys, heart 

 and spleen were also affected in some cases. Two control animals 

 fed with similar grain without added selenium developed nor- 

 mally. 



The minimum lethal dose of selenium for rats, rabbits, horses 

 and mules appears to be of the order of 1-5 or 2 mg. per lb. of 

 body weight, for cattle 4-5-5 mg. per lb. of body weight, and for 

 pigs between 6 and 8 mg. per lb. of body weight. 



By the continued administration of small doses of selenium 

 to horses Miller and Williams (19406) produced symptoms 

 similar to, though not so striking as, those observed in chronic 

 alkali disease under natural conditions. These symptoms included 

 listlessness, loosening of hair in the mane and tail, softening of 

 the horny wall of the hoof, and lesions in the liver, heart, 

 kidneys and spleen. 



It being thus clear that ' alkali disease ' results from poisoning 

 by grain or forage containing selenium, it is important to know 

 whether there are differences in the selenium-absorbing capacity 

 of different plants. There is no doubt that this is very much 

 the case. Byers (1935) found notable differences in the selenium 

 content of plants occurring naturally on seleniferous soils, while 

 Hurd-Karrer (1935) also found marked differences in the 

 selenium content of crop plants grown on artificially selenized 

 soils. Thus Miller and Byers (1937) record a selenium content of 

 1110 p.p.m. in Astragalus bisulcatus and one of only 45 p.p.m. 

 in wheat grown in the same area. In another area they found 

 1250 p.p.m. of selenium in A. bisulcatus, but only 3 p.p.m. in 

 A. missouriensis . Byers had earlier found as much as 4300 

 p.p.m. of selenium in A. bisulcatus, while relatively enormous 

 quantities of selenium have also been found in other species of 

 Astragalus, as, for example, 5560 p.p.m. in A. ramosus and 

 1750 p.p.m. in A . pectinatus . On the other hand, A. missourien- 

 sis, A . mollissimus and A . drummondii absorb only little selenium. 

 Prairie grasses in general have a very low capacity for absorbing 

 selenium ; thus Andropogon scoparius (little blue-stem) was found 

 to contain only 0-8 p.p.m. of selenium. 



