REACTION OF CELLS 79 



bacteria does not, therefore, depend in a sensible 

 degree on their different ability to resist the de- 

 structive action of the poison. Instead of this a 

 certain fraction of the bacilli still living dies in one 

 second, independent of the time during which they 

 have been in contact with the poison. 



In order to understand this we make the follow- 

 ing observation. In a i per cent solution of acetic 

 acid only i per cent of the molecules are in a 

 dissociated state (at 25 C). It is not the same 

 molecules which remain constantly in the dissociated 

 state, but every molecule is dissociated during one 

 unit of time and undissociated during ninety-nine 

 units. The reactivity of the ions is much greater 

 than that of the whole molecules. We suppose for 

 simplicity that the ions alone react. Then at any 

 moment only 1 per cent of the acetic acid 

 molecules are in state to react. The proteids con- 

 tained in the living protoplasm are amphoteric 

 electrolytes. Only a thousandth part (we suppose 

 this figure for simplicity) of the proteid molecules 

 has split off its H-ions, and perhaps only a millionth 

 part its OH -ions. Then probably one part in a 

 thousand millions has split off both its H-ions and 

 its O H-ions. Perhaps it is only living protoplasm 

 containing one or two such ions which is able to 

 react with the poison. At every moment only this 

 small fraction is open to attack, and at this moment 

 a molecule of poison must be present for the cell 

 proteid to be destroyed. Probably the cell only 

 dies after a certain number of its proteid molecules 



