TOXICITY OF ACIDS TO INFUSORIA 87 



up of the edge of the cell. This shrinkage is probably a purely 

 osmotic phenomenon, for it also occurs in a balanced salt solution 

 such as diluted sea-water. The fat-soluble acids when acting 

 alone produce a less well-marked coagulation and a greater disin- 

 tegration ; this is probably due in part to their power of dissolving 

 lipoids and in part to the low concentration of the H ion present 

 in the solutions. Otherwise the results are similar to those 

 described for acetic. 



It is especially noteworthy that in the efficiently balanced 

 mixtures of salt and acid the protoplasm remains for a long time 

 apparently normal, as if the acid were unable to penetrate the 

 surface. The swelling which eventually appears in most of the 

 mixtures is in all likelihood due to the small amount of acid which 

 is able in spite of the salt protection gradually to penetrate the 

 surface. Only in the presence of very small quantities of salt can 

 enough acid penetrate to bring about coagulation. With more 

 dilute acid solutions a dehydrating effect of the salts would prob- 

 ably be evident, and in the present experiments it may be indi- 

 cated by the delay in the early development of the swelling. 



DISCUSSION 



There are in the literature a number of experiments illustrating 

 the antagonism existing between acids and neutral salts, both in 

 living and in non-living systems. Loeb- found that certain concen- 

 trations of acids (CO2, HCl, acetic, butyric) kill Fundulus adults 

 apparently by altering the gill epithelium, and that the solutions 

 are rendered almost harmless by the addition of NaCl or CaCli. 

 The effective concentration of NaCl is ten times that of CaCl. 

 (in terms of molecular concentration). Similarly, the toxic 

 action of isotonic sugar solutions upon Fundulus adults occurs 

 only when the medium has become acid, and is greatly delayed 

 by the presence of neutral salts (Loeb^) . With Fundulus embryos 

 Loeb* found that the intake of water induced by acetic acid 

 N/333 is greatly diminished by M/2 balanced salt solution. The 

 toxicity of the acid to the embryo (as indicated by coagulation of 

 the tail within the egg membrane) is also greatly lessened by the 

 addition of neutral salts, probably because they hinder the diffu- 



