R. D. HOTCHKISS 



we conclude that tyrocidine kills bacteria because it brings about a 

 cytolytic injury to their cell membranes. 



Some thirty antiseptic substances, including mercury deriva- 

 tives, halogens, oxidizing agents, formaldehyde, dyes, etc., were able 

 to kill or completely repress growth of staphylococci without releasing 

 cell constituents. The increase in cellular permeability, which is often 

 supposed to occur generally with death, was not noted at all, and 

 certainly cannot, for these cells at least, be confused with the clear-cut, 

 almost instantaneous, physical change that accompanies killing by 

 tyrocidine. 



However, the further analysis of the bactericidal effect is of 

 interest to us as cytochemists. It is not hard to explain a drop in the 

 respiratory rate in these dead cells. With the seepage of coenzymes, 

 activating ions, and intermediates out of the cells, there occurs an 

 enormous "dilution" of the multicomponent respiratory systems. It 

 is well known that dilution of a reacting system decreases its rate more 

 or less according to an exponential function of the degree of dilution, 

 in which the exponent is the number of reacting components. There- 

 fore dilution of, say, a three-component system, can be tremendously 

 "inhibitory" in its effect. It is actually found that the residual 

 metabolism is more dependent upon the volume into which this dilu- 

 tion takes place than upon the concentration of cytolyzing agent. 

 Accordingly, it is unnecessary to suppose that enzymes are inactivated 

 by the minute amounts of tyrocidine needed to kill bacteria. 



Hydrolytic enzymes such as the peptidases, phosphatases, and 

 nucleosidases, however, are less affected by dilution than are respira- 

 tory enzymes, since the hydrolytic systems contain fewer components, 

 and the concentration of one of these, water, is scarcely changed by 

 dilution. In harmony with this, bacteria cytolyzed by tyrocidine 

 begin to undergo enzymic post-mortem changes which result in the 

 liberation of soluble degradation products, and with some species, but 

 not universally, may progress to actual bacteriolysis, i. e., partial or 

 even complete clearing of the suspension. These effects, if not avoided 

 by keeping the temperature low, or by adding enzyme poisons, may 

 obscure the observation of the initial cytolytic injury. It is apparent 

 that tyrocidine does not inactivate these hydrolytic enzymes. Does 

 it activate them, or why do they begin to work after the cytolytic 

 death? Only a few experiments with certain phosphatases have so 



