METABOLIC GRADIENTS OF VERTEBRATE EMBRYOS. 3 



hydroxide, and sodium hydroxide. These three reagents were 

 selected because of their high disintegrating powers, probably 

 due to their alkalinity. Owing to the diaphanous nature of the 

 chick embryo, particularly -in early stages, the occurrence of 

 disintegration changes cannot be detected unless they are well 

 marked, hence the necessity for agents of the above character. 

 It is also necessary to employ these agents in rather strong con- 

 centration so that death will occur in a relatively short time, 

 for the more slowly the death changes take place the less detect- 

 able are they. Potassium cyanide was used in about 1/50 mol. 

 concentration, dissolved in 0.9 per cent, salt solution. The 

 ammonium hydroxide was made by adding two or three drops of 

 strong ammonia to 50 to 100 cc. of 0.9 per cent, salt solution. A 

 i per cent, solution of sodium hydroxide was prepared in 0.9 per 

 cent, salt and several drops of this were added to the watchglass 

 containing the embryo and half filled with salt solution. In some 

 cases embryos were stained with neutral red before applying the 

 sodium hydroxide; this is a very convenient procedure as the 

 death of any part of the embryo is evidenced by a change of 

 color in the dye from red to yellow. 



The results in all three reagents were identical. Potassium 

 cyanide and ammonia are believed to penetrate organisms readily 

 but sodium hydroxide does not penetrate until death has occurred. 

 Death differences cannot therefore be ascribed primarily to 

 differences in rate of penetration of the agents for agents which 

 enter readily and those which do not enter during life kill in 

 the same differential manner. Further, since the agents were 

 made up in salt solution, isotonic with the fluids of the chick, 

 the contention of Wilson ('25) that the disintegration of animals 

 in toxic solutions is due to the hypotonicity of such solutions 

 cannot apply here. The disintegration of chick embryos in such 

 isotonic solutions presents no noticeable differences from the 

 disintegration changes of Planaria, for instance, in hypo tonic 

 toxic solutions. 



Unless specifically stated otherwise several embryos of each 

 stage have been observed. The death gradients in different 

 individuals of the same stage of development are always similar 

 with such variations as are stated in the following descriptions. 



