136 EXTERNAL FACTORS III. 8 



of the anion, antitoxicity with that of the cation. Ions of the 

 same valency are not, however, necessarily equally antitoxic 

 (Loeb and Gies, Lillie, Mathews), and sodium sulphate, as we 

 have seen, may act as an antidote to the chloride (Moore). 

 Mathews has accordingly sought for the cause of toxicity in 

 another physical property, the decomposition tension of the salt, 

 and has certainly succeeded in showing that the poisonousness 

 of solutions to the eggs of Fundulus varies inversely with the 

 decomposition tension, and that a similar relation holds good in 

 certain other cases. 



Lillie argues that a physiologically balanced solution is 

 necessary, one in which the electrolytes are in a state of 

 chemical equilibrium with the necessary ion-proteid compounds 

 in the tissues. Solutions which only contain some of these 

 substances, or solutions (for example, non-electrolytes) which 

 contain none, are poisonous, because they permit of the outward 

 diffusion of the needful ions. 



It must be pointed out, however, that this explanation will 

 not fit the cases where the embryo develops perfectly well in 

 fresh water (Fundulus) or in distilled water (the Frog), and that 

 some other reason must be found for the poisonous effect of 

 cane-sugar upon the latter. The whole question, however, is one 

 which belongs more properly to the province of pharmacology. 



Poisonous although these salts are, the embryo can still be 

 acclimatized to them. C. B. Wilson placed the unsegmented 

 eggs of Amblystoma, Rana, and Chorophilus in a 0-05 % solution 

 of sodium chloride ; after twenty-four hours they were removed 

 to 0-1 %, and then successively to stronger solutions by incre- 

 ments of 0-1 % until 1-0% was reached, a concentration which 

 quickly causes death under ordinary circumstances. In this 

 case, however, development was normal, and the larvae hatched 

 out and lived for some time. 



The distortions of development which solutions of salts and 

 other substances call forth in Amphibian embryos find a parallel 

 in the malformations which Herbst has produced in Echinoderm 

 larvae (Echinus, Sphaerechinus) by similar means; as in the 

 former case, the results were at first assigned to the increased 

 osmotic pressure of the media. 



