TOXICITY OF ACIDS TO INFUSORIA 91 



of such a salt as CaClo for possession of the cell surface. The liquefy- 

 ing action of more dilute acids on gelatin and similar gels might, 

 as Loeb suggests, be limited by the ionization or specific solu- 

 bility of the Na- or Ca-colloid salt. The penetration of the acid 

 into the cell might be prevented by such changes in state at the 

 surface as -are suggested by Osterhout,''! Lillie,"'^-*^ Spaeth, ^^ and 

 Fenn.^2 Sodium salts seem to promote the fluidity or degree of 

 hydration and so the permeability of the membrane to water- 

 borne substances, calcium salts to promote aggregation with 

 dehydration of the surface layer and so impermeability (although 

 Ca in excess will coagulate the membrane and so render it more 

 permeable). Clowes^- ^' i*' has suggested that the increased aggre- 

 gation of the film produced by CaCU is due to an increase in the 

 amount of water-insoluble soap in the most external boundary 

 phase of the protoplasmic emulsion; such a change would be 

 associated with lessened permeability to water-borne substances. 

 The liquefaction induced by NaCl would be due to a decrease 

 in the amount of the oil-miscible compound (lipoid or soap and 

 an increase in the amount of the water-miscible compound (e.g., 

 Na-soap); this change would lead to a greater permeability 

 toward water-borne substances. These various explanations do 

 not seem to be mutually exclusive although in some cases they do 

 not apply equally well Additive effects of various kinds must 

 also enter. 



In my experiments with Paramecium, Ca is a more efficient 

 antagonist than NaCl and at a much lower concentration. This 

 is true especially with the less fat-soluble acids. With Euplotes 

 a similar difference is observed. At high concentrations NaCl 

 completely loses its power to protect Euplotes against the non- 

 fat-soluble acids, although at low concentrations it is fairly 

 efficient. Against several fat-soluble substances NaCl proves 

 to be an efficient antagonist, even at high concentrations, in spite 

 of the fact that by itself it is very toxic to Euplotes. If we com- 

 pare butyric with HCl in equitoxic concentrations, w^e find that 

 NaCl at its best prolongs the life of Paramecium four times in 

 butyric and three times in HCl; that of Euplotes ten times in 

 butyric and once in HCl. That is, the efficiency of NaCl is 



