When you say, in the February number, that "none of Cohn's experiments prove that bacteria ever interfere with life," you give utterance to the plain truth in regard to all other experiments, and theories on this subject. Bacteria can only live and increase upon inert matter. In healthy trees, the rapid passage of the fluid containing them through the fibrous tissues will break and destroy the simple and very delicate organism. The increase of these bacteria is the first indication of the suspension of vital activity in trees and vegetables. The virus passed into healthy pear trees by inoculation from those diseased is not the virus produced by bacteria ; but the poison originates in vitiated sap. Now, this sap is simply that which has accumulated in the tree and its branches since the fall of the leaf, and has not been aerated, but frozen and devitalized during the winter. Remaining in the tree in spring, it clogs the channels and disturbs the whole economy of the structure. Warm weather and a mingling of this inert fluid with the active sap causes a great increase of bacteria - the operating principle in all fermentation - and when the disease reaches a certain stage it becomes apparent in suddenly blackened leaves and withering branches.

This is the only theory that can satisfy all the requirements of the case.

There must be some error about bacteria abounding in the circulatory vessels of human beings. They are not in the blood, and can be found nowhere but in the large intestines. Infusoria are, doubtless, in the human body, but they possess an independent motion, and differ widely from bacteria.