Formation of Embryonic Structures. 



93 



A study of the bone marrow in these animals shows an effect 

 comparable to that of benzol. There is early destruction of the 

 cells of the granulocyte series and in some animals an extra- 

 ordinary depletion of the bone marrow. Animals which partially 

 recovered from the initial injection and were then killed, showed 

 active regenerative changes in the bone marrow. 



There is a possibility that these effects may have been due to 

 the chlor-benzine or nitro-benzine used as a solvent in German gas 

 shells, and carried over in the distillate used for injection. In 

 view of the small amount of such impurity present, this does not 

 seem likely, but there was no opportunity to repeat the experi- 

 ments with dichlorethylsulphide completely freed from this solvent. 



The experiments were carried out in collaboration with Capt. 

 Morgan B. Vance, M.C., at Hanlon Field, Chaumont, France. 



54 (1429) 



J 



Developmental rate and the formation of embryonic structures. 



By Charles R. Stockard. 



[From the Department of Anatomy, Cornell Medical School, New 



York City.] 



The eggs of different species develop at specifically charac- 

 teristic rates. These rates vary for a given species within certain 

 limits. Variation in the direction of increased rate is far more 

 limited and more difficult to bring about experimentally than is 

 the opposite variation towards a decreased or slower rate. 



The slight acceleration of developmental rate that may be 

 induced in early embryos does not seem to cause any marked 

 deviation from the normal course of development, on the contrary 

 such embryos are unusually well developed. It might be said 

 that the ideal rate of development is probably somewhat faster 

 than the so-called normal average usually followed. In other 

 words, the normal conditions of development are not entirely the 

 best possible conditions. 



The limits of retardation in developmental rates are extremely 

 wide. The rate may be slowed down to almost zero or develop- 

 ment may actually be to all appearances stopped for long or short 



