Respiration

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Abstract
A preceding paper (Cook, 1925-26) has discussed the general effect of salts of copper and of other metals on the respiration of Asper- gillus niger. It was demonstrated that the toxic action followed cer- tain definite laws and could be formulated in a mathematical system. Mention was made of a peculiarity in the case of copper, wherein this element differed from the others studied. When copper chloride acts on Aspergillus niger there is at first no change in the rate of respira- tion, but later the production of carbon dioxide decreases in the man- ner characteristic of the action of all the heavy metals Studied. The time which elapses between the introduction of the copper and the beginning of the drop in respiration rate has been termed the latent period. Save where otherwise stated, the methods used in investigating this latent period were the same as those used in studying the other toxic effects of copper, mercury, and silver. All work on respiration was done by the indicator method with the Osterhout respiration machine as previously described. Fig. 1 shows a typical curve for the effect of copper chloride, including latent period and subsequent drop. It might appear that the figure does not consist of a straight line followed by a distinct and clearly differentiated drop, but that it is really a continuous curve starting with the introduction of the cop- per, failing imperceptibly for a while and then with increasing velocity. In this case the curve should show a sharp bend toward the end of
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