196 
Journal of Agricultural Research 
Vol. XXX, No. 2 
had been deficient in either copper, 
manganese, or zinc. The author is 
seeking a definite answer to this ques¬ 
tion by experiments both with plants 
and with small animals. It has been 
known for a long time that copper is of 
common occurrence in the tissues of 
land and marine animals. It is stated 
that copper replaces the function of 
iron in the metabolism of some of the 
lower forms of animal life. It is a well 
known fact that inorganic compounds 
of copper, manganese, and zinc have 
important catalytic functions and it is 
not unreasonable to assume such a r61e 
for the organic colloidal complexes of 
these metals in the metabolic processes 
of plants and animals. 
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O 
