1. The effect of the heavy metals on the respiration of Aspergillus niger is to cause the rate of carbon dioxide production to decrease from the first or to increase and subsequently diminish.

2. The speed of the toxic action varies as a constant power of the concentration.

3. The temperature coefficient of the toxic action is between 1.5 and 2.

4. An hypothesis is advanced to account for the action of the heavy metals, by means of which the experimental results may be accounted for. It is assumed that the metal is activated by a chemical combination with a cell constituent. This active compound alters the velocity constants of the normal respiratory reactions, and thus causes the observed changes in the rate of carbon dioxide production.

This content is only available as a PDF.