1917] Forbes: Irrigation Effects of Copper Compounds Upon Crops 461 



Bacilli of various species reacting upon human health are very 

 sensitive to the action of soluble copper salts. For instance, in 

 distilled water "one part copper in 16,000,000 parts water killed 

 typhoid bacilli in two hours. In copper solutions made up with 

 tap and sea water, the action was still marked, but less vigorous 

 than in distilled water. ' ' ^- Moore and Kellerman state that one 

 part of copper sulphate to 100,000 parts of water destroys 

 typhoid and cholera germs in three to four hours.^^ In milk 

 supplies as little as one part of copper salts in 2,000,000 of water 

 acts as an antiseptic against putrescent bacteria.^* It seems, 

 therefore, that there is a possibility that the amounts of copper 

 observed in ditch and well-waters in the district may have an 

 antiseptic effect upon malignant germs, more particularly typhoid 

 fever, likely to occur in the district.^" 



Amounts and Significance of Copper in Aerial Vegetation 



The amounts of copper found in aerial parts of vegetation 

 within the district are small, ranging from a trace to 7.6 parts 

 copper in 1,000,000 of dry matter and averaging 3.41 parts. 

 Miscellaneous cultures in water, potted soils, and plots gave 

 larger amounts of copper which, however, were associated in 

 most cases with toxic effects. Table 30 (p. 462) contains a sum- 

 mary of these data. 



Even allowing for errors of method and of analysis, the 

 European figures (3) seem excessively high, although the woody 

 character of most of the samples was for the most part very 

 different from that of the tender crop plants of the Arizona series. 



Little can be said as to the toxic effects of the copper ob- 

 served in aerial plant parts in the Arizona samples. The yellow 

 striping of copper-poisoned corn is probably a general symptom 

 of malnutrition to be attributed to the effect of copper upon root 

 systems rather than upon leaves and stems. In rare instances, 

 however, beans and squash in water culture showed dark green 



i2Biocliem. Jour., Aug., 1908, pp. 319-323. 



13 U. S. D. A. Bur. PI. Ind., Bull. 64, p. 43. 



14 Jour. Ind. and Eng. Chem., Sept., 1909, p. 676. 



15 See Bibliography, p. 487, references 3, 20, 21, 2^ 



