396 ANIMAL BIOCHEMISTRY 



included in this miscellaneous group because they are of practical 

 concern as poisonous materials encountered in human affairs. 



Aluminum seems to be universal in plants and animals without 

 important roles in either and with no known function in the latter. 

 Since diets free of aluminum have not been devised, one cannot say 

 categorically that this element is not essential. Certainly there is no 

 likelihood of a deficiency since all tissues contain it. Large quantities 

 of aluminum interfere with phosphate utilization, but there seems to 

 be no danger of this antagonism even when aluminum vessels are 

 used in food processing. 



Arsenic is also present in all soils, sometimes in large quantities. 

 However, the levels taken up by plants are too small to harm animals. 

 Soil concentrations may be high enough to poison plants, but the 

 limited growth in such cases seems to be harmless to grazing animals. 

 Residues from sprays and industrial dusts sometimes become toxic, 

 and animal poisoning is occasionally reported. The introduction of 

 other pesticides, in part replacing those based on arsenic, has reduced 

 this problem. 



Beryllium is a rare component of the earth's crust that finds indus- 

 trial uses. Formerly, the element was employed in the phosphors 

 lining fluorescent lamps. However, beryllium compounds from bro- 

 ken lamps prevented the healing of wounds. Moreover, inhalation of 

 beryllium as dust leads to non-healing injuries of the lungs. Since 

 the toxicity is persistent, use of the element in household lamps has 

 been discontinued. However, metallurgical and other industrial 

 applications still pose problems. Be++ is antagonistic for Mg+ + 

 and prevents activation of enzymes by the latter ion. Hence beryllium 

 poisoning may be based on this sort of interference. 



Barium is another rare element but, as distinguished from beryl- 

 lium, is widespread and is normally found in bones. Barium also 

 occurs in soft tissues, especially one of the layers of the eye of higher 

 animals. The ion is quite toxic but except in traces is not encoun- 

 tered in soluble form outside the chemical laboratory or industry. 

 One unconfirmed report states that Ba++ is essential for the proper 

 distribution of calcium in the skeleton. 



Boron is essential to a variety of plants and occurs in animals but 

 without a known role. Although not particularly toxic because it is 

 readily excreted via the kidneys, accidental ingestion of large quan- 

 tities of boric acid or treatment of extensive burns with this com- 

 pound will produce symptoms. Adult human beings normally ingest 

 10 to 20 mg. of boron daily without effect, so even accidental poison- 



