April 15, 1921] 



SCIENCE 



353 



It has been found that the electrical resist- 

 ance of this plant is an excellent index of 

 what may be called its normal condition of 

 vitality. Agents which are known to be in- 

 jurious to the plant change its electrical 

 resistance at once. If, for example, it is 

 taken from the sea water and placed in a 

 solution of pure sodium chloride it is quickly 

 injured, and if the exposure be sufficiently 

 prolonged it is killed. During the whole time 

 of exposure to the solution of sodium chloride 

 the electrical resistance falls steadily until 

 the death point is reached; after which there 

 is no further change. If we study the time 

 curve of this process, we find that it corre- 

 sponds to a monomolecular reaction (slightly 

 inhibited at the start). 



This and other facts lead to the assump- 

 tion that the resistance is proportional to a 

 substance, M, formed and decomposed by a 

 series of consecutive reactions. On the basis 

 of this assumption we can write an equation 

 which allows us to predict the curve of the 

 death process under various conditions. This 

 involves the ability to state when the process 

 will reach a definite stage, i.e., when it will be 

 one fourth or one half completed. This can 

 be determined experimentally with consider- 

 able accuracy. 



This curve is of practical, as well as of 

 theoretical importance, since it allows us to 

 compare the degi-ee of toxicity of injurious 

 substances with a precision not otherwise 

 attainable. The best way of doing this is to 

 proceed as a chemist might in such cases and 

 express the degree of toxicity by the velocity 

 constants of the reaction (i.e., of the death 

 process) under various conditions. 



From this point of view we must regard 

 the death process as one which is always 

 going on, even in an actively growing normal 

 cell. In other words the death process is a 

 normal part of the life process. It is only 

 when it is unduly accelerated by a toxic sub- 

 stance (or other injurious agent) that the 

 normal balance is disturbed and injury or 

 death ensues. 



If we wish to put this into chemical terms 

 we may say that the normal life process con- 



sists of a series of reactions in which a sub- 

 stance O is broken down into S, this in turn 

 breaks down into A, M, B and so on. Under 

 nomal conditions M is formed as rapidly as 

 it is decomposed and this results in a con- 

 stant condition of the electrical resistance 

 and other properties of the cell. When, how- 

 ever, conditions are changed so that M is 

 decomposed more rapidly than it is formed 

 the electrical resistance decreases and we find 

 that other important properties of the cell are 

 simultaneously altered. 



Hence it is evident that injury and death 

 may result from a disturbance in the relative 

 rates of the reactions which continually go on 

 in the living cells. 



It is evident that we can follow the process 

 of death in the organism in the same manner 

 that we follow the progress of a chemical 

 reaction in vitro. In both cases we obtain 

 curves which may be subjected to mathe- 

 matical analysis, from which we may draw 

 conclusions as to the nature of the process. 

 This method has been fruitful in chemistry 

 and it seems possible that it may be equally 

 useful in biology. 



If we suppose that resistance depends on a 

 substance, M, it may be desirable to discuss 

 briefly certain assumptions which have been 

 made in regard to it. The protoplasts of 

 Laminaria are imbedded in a gelatinous 

 matrix (cell wall) which offers about the same 

 electrical resistance as sea water or dead 

 tissue. Since the electrical resistance of the 

 living tissue is about ten times as great as 

 when it is killed it is evident that the living 

 protoplasm must be responsible for the in- 

 creased resistance. The living cells consist 

 for the most part of a large central vacuole 

 surrounded by a delicate layer of protoplasm: 

 the sap which fills the vacuole seems to have 

 about the same resistance as the sea water. 

 The high resistance of the living tissue must 

 therefore be due to the layer of protoplasm 

 surrotmding the vacuole, a layer so extremely 

 thin as to be comparable to what is commonly 

 called the " plasma membrane." Since the 

 current is due to the passage of ions through 



