THE PERMEABILITY OF CELLS 513 



3. Analytical (chemical or otherwise) a. By analysis of cells 

 themselves. 



h. By analysis of medium (chemically, or by determining 

 freezing point or electrical conductivity) after diffusion into the 

 cell has taken place. 



c. By analysis of the medium after diffusion from the cell has 

 taken place. 



4. Conductivity [of blood corpuscles (Stewart, Tangl and 

 Burgarszky, and Roth) or of eggs (McClendon)]. 



5. Alteration of function (on the assumption that to affect 

 a cell the substance must enter). 



a. Test by toxicity. 



h. Test by narcosis (Overton). 



c. Test by change in manner of response to stimuli (Loeb, 

 Dynamics of Living Matter, p. 842, New York, 1906). 



d. Test of effectiveness in causing artificial parthenogenesis 

 (Loeb, J., Chemische Konstitution und physiologische Wirksam- 

 keit von Sauren. Biochemische Zeitschrift, 15, p. 254, 1909). 



No one of the above methods can be claimed as universally 

 better than any of the others. Recent researches have exposed 

 sources of error in the application of the plasmolytic method 

 (Osterhaut, '08). Mass analyses of cells give. us no hint as to 

 the location of the substance in the cell or the state in which it 

 is present, in solution or in combination. 



The evidence (pp. 543-546) in the case of the inorganic hydrox- 

 ides shows that these alkalies may produce functional changes and 

 death of Paramoecium without entering in sufficient quantity to 

 affect granules stained in neutral red within the cell, and its 

 effect must be on the membrane. Hoeber regards the surface 

 of the cell as the point of attack of the strongly dissociated sub- 

 stances in general. Only after the cell surface has been funda- 

 mentally modified does the reagent pass in. 



Whenever applicable the observational methods are most useful 

 in studying problems in permeability, for they not only answer 

 the general question concerning penetration of the substance in 

 question, but also enable us to locate the reagent in the cell and 



