EXOGASTRULATION AM) RELATED MODIFICATIONS. 



81 



sary to determine whether lithium can be made so far effective 

 as to cause ectoderm to appear at the basal pole, etc. 



Normal E 

 apical 



a -i 



Lithiurn L VTI b *~ i_i o 

 a p \ c a I 



Ect odLerm 



hi* " f 

 i-3 at 





Ch d o d-e-v 





rne 



b' 



h -L 



I/ 



basal k 



Kir.. 13. Diaxrarn showinx tlie changed proportions of parts in a lithium 1-1: 



as compared with a normal embryo (left), and the typical reversal oi ' 

 lii lity (the arrows), a-b in normal, b'-a' in lithium embryos. Tl 

 ill pressing concentration of lithium is to shift the embryo to the right. An .. 

 riatiiix ax-rit would alter embryonic proportions in the opposite din . timi. 



3. Non-specificity of Lithium Effects. 



(a) Changes of Proportions of Parts. A great vark-t y ( if ( la-mi- 

 ca 1 agents and physical conditions have been employed in ex- 

 perimental embryology to cause general death and disintegration, 

 general inhibition of development, differential (/... lorali/<l 

 inhibition, and, in the minimal effective concentration-, differen- 

 tial acclimation effects. The striking fund.niient.il -imilarity of 

 teratological forms produced by di\> genl ial cmiditions is 

 too remarkable to be insignificant. Then- can In- no ma tera- 

 togenic substance or condition \vho>r rt'U-ct dilltr- -h.irpl\- in 

 kind from others. Though each may have it- <>\vn mode of 

 attack, the end result is in general injuriou- and inhibitory or 

 accelerative, according to the p\\ti of resistance of different 

 levels along the metabolic ijMdient. The only -peciticity of 

 lithium effect seems to lie in the higher re^am.il differential 

 -ii-ivptibility of many organi-m- io it ; lithium ha- a particularly 



