February 2, 1917] 



SCIENCE 



99 



It is a very striking fact that all three of 

 these methods agree with those already de- 

 scribed in showing that physiologically bal- 

 anced solutions preserve normal permea- 

 bility, while NaCl causes a rapid increase, 

 and CaCl, an initial decrease, followed by 

 an increase of permeability. 



This general agreement can not but in- 

 crease our confidence in the conclusion that 

 permeability and antagonism are intimately 

 connected. 



Further studies have shown that permea- 

 bility serves as a delicate indicator of what 

 we may call the vitality of the organism. 

 By this is meant a condition of normal 

 health and vigor and the ability to resist 

 unfavorable influences. An organism 

 which has normal permeability (as shown 

 by determining its electrical conductivity) 

 behaves normally in all respects and lives a 

 normal length of time under laboratory 

 conditions, while one which has abnor- 

 mally high permeability behaves abnor- 

 mally and does not live the normal length 

 of time. Hence it would appear that we 

 can treat vitality quantitatively, for if the 

 vitality of a large number of organisms is 

 measured in this way we obtain a variation 

 curve: this indicates that vitality may be 

 treated in the same manner as any other 

 character (as, for example, length or 

 weight). 



Moreover, since increase of permeability 

 indicates injury, we have a method of meas- 

 uring injury and of distinguishing quanti- 

 tatively between temporary and perma- 

 nent injury. It is found that great fluctua- 

 tions of permeability are possible without 

 permanent injury. These fluctuations may 

 control the metabolism of the cell. 



These studies show that all agencies 

 which sufficiently alter the normal permea- 

 bility of the protoplasm (such as poisons, 

 excessive light, heat, electric shock, severe 

 plasmolysis, mechanical shock, partial drj^- 



ing, lack of oxygen, etc.), shorten the life 

 of the organism. This is a very striking 

 fact and its significance seems to be unmis- 

 takable. It indicates that permeability is a 

 delicate and accurate indicator of vitality. 

 An analysis of the factors which con- 

 trol permeability has been attempted in 

 subsequent studies. The changes in the 

 resistance of tissues placed in mixtures of 

 NaCl and CaCl, have been carefully deter- 

 mined. These are shown in Fig. 1. A 

 glance at the figure suggests that there are 

 two processes, one of which causes a rise, 

 the other a fall of resistance. It is natural 

 to suppose that these are chemical in nature 

 and we may assume that they are consecu- 

 tive reactions by which a substance M, 

 which determines the resistance of the pro- 

 toplasm, is formed and broken down ac- 

 cording to the formula 



It may be assumed that M is a substance at 

 the surface of the cell which offers resist- 

 ance to the passage of ions. 



It is evident that if the first reaction 

 A-^M is more rapid than the second, M 

 will be formed more rapidly than it is de- 

 composed and will increase in amount. 

 Eventually, as the supply of A becomes ex- 

 hausted, the formation of M will go on 

 more and more slowly, so that it will no 

 longer keep pace with the decomposition. 

 The amount of M will then diminish until it 

 finally disappears or reaches a fixed mini- 

 mum (this corresponds to the death of the 

 tissue). It is evident that if the relative 

 velocities of the two reactions A —^M, and 

 M — » 5 be properly varied the curves of 

 resistance will rise and fall rapidly or 

 slowly in the manner shown in Pig. 1. It 

 can be shown that these assumptions en- 

 able us to account for all the experimental 

 curves. 



A point of importance is that the veloci- 



