EXTERNAL FACTORS 



III. 7 



a result which is further corroborated by the constancy in the 

 relative toxicities of the bases and the acids in the case of the 



FIG. 66. Frog embryos grown in isotonic solutions of, A, sodium 

 chloride (-625%) ; B, cane-sugar (6-6%) ; c, dextrose (34%) ; and, D, urea 

 (1-14%). In A the medullary folds are closed but the blastopore open ; 

 in B the medullary groove is open but the blastopore closed ; in c de 

 velopment is normal, but retarded ; in D development is normal, both in 

 form and rate, though the embryos die soon after the stage shown in 

 the figure. 



FIG. 67. A. Longitudinal section of a Frog embryo grown in a 45% 

 solution of lithium chloride. The medullary groove is open, except in 

 front and behind. The notochord is bent in several places and the gut 

 roof much crumpled. B. Longitudinal section of a Frog embryo grown 

 in a 6-6% solution of cane-sugar. The medullary groove is open, except 

 in front, the cells in its floor degenerating. The gut roof is incomplete in 

 part and there is an evident neurenteric canal. 



monobasic salts. The observed deformities are therefore to be 

 attributed to some other chemical or physical property of 



