would appear to me as inevitable, that living substance contains in itself a certain even though a very slight quantity of oxygen, which in low temperature is greater, in a high temperature less, the recovery from narcosis, when oxygen is withheld, is not at all surprising. The comparatively rapid setting in of depression in narcosis finds a simple explanation in the _violent_ manner in which the oxydative breaking down, notwithstanding the presence of oxygen, is suddenly suppressed by the flooding by the narcotic. Finally, this view receives unlooked-for support by a group of facts which at the first glance would appear to bear no relation whatever to the process of narcosis. [218] Compare lecture V; lecture VII. [219] The investigations have not yet been published. [220] _Fr. W. Frölich_: “Das Sauerstoffbedürfniss des Nerven.” Zeitschr. f. allgem. Physiol. Bd. III, 1904. In a series of investigations on the mechanism of movement in naked protoplasm,[221] I have pointed out the rôle played by oxygen in the genesis of the amœboid protoplasm movement. We can distinguish two antagonistic phases in the movement of amœboid cells, the expansion phase and the contraction phase. The first consists in an increase, the latter in a diminution of the surface, the mass remaining the same. The expansion phase is manifested in the stretching out of the pseudopods by a centrifugal outflowing of the protoplasm into the surrounding medium, the contraction phase by the indrawing of the pseudopods by the centripetal inflowing of the protoplasm to the cell body. In total contraction, such as occurs, for instance, in strong excitation following stimuli, the cell body becomes ball shaped. In local contraction of the long thread or net-shaped outstretched pseudopods of the sea rhizopoda, the protoplasm of the retracting pseudopod forms balls and spindles. Considered from a physical point of view the expansion phase of amœboid movement is an expression of decrease, the contraction phase an increase of the surface tension. I have shown that the factor which under physiological conditions decreases the surface pressure and thereby brings about the expansion phase is the introduction of oxygen into the living substance. With removal of oxygen the stretching out of the pseudopods ceases. The cell gradually draws in all pseudopods and assumes the shape of a ball. On the reintroduction of oxygen the outflow of the pseudopods begins anew. This fact can be observed in all amœboid cells. When, therefore, consumption of oxygen and oxydative changes is suppressed during narcosis it is to be expected that all naked protoplasm masses by being narcotized lose their capability of assuming the expansion phase of movement and contract into the shape of balls. Experimentation confirms this deduction in the most striking manner. When amœbæ are placed in a drop of water under the microscope in a gas cell through which air