22 LIBBIE H. HYMAN. 



results agree with my findings that the embryonic is more 

 susceptible than the extra-embryonic portion of the blastoderm 

 and the anterior part of the primitive streak more susceptible 

 than its posterior part. 



More numerous have been the attempts to modify the develop- 

 ment of the chick by various chemicals. Fere ('94, '990) exposed 

 eggs to the vapors of ethyl and other alcohols before incubation, 

 and reported the following abnormalities: blastoderms without 

 embryos, arrest of development of the amnion, cyclopia, absence 

 of the eyes, defective heads, atrophy of the head, spina bifida, 

 absence of somites, duplicity of the heart. He also ('996) tried 

 the effect of exposure to the vapors of ammonia before incubation. 

 Ammonia was found to be exceedingly toxic; one half hour ex- 

 posure yielded blastoderms with embryos. After fifteen minutes 

 exposure, defects similar to those obtained with alcohol resulted. 

 Reese ('12) tried the effect of various narcotics on the develop- 

 ment of the hen's egg but gives no details beyond the statement 

 that abnormalities were produced. Stockard ('14) treated the 

 egg with various chemicals and states as did Dareste that their 

 action is not specific. Eggs were exposed to the vapors of 

 alcohol and ether before or during incubation. The treated 

 embryos tended to be small and developed more slowly than the 

 controls. Among the defects noted were: blastoderms without 

 embryos, small and reduced embryos with defective brains and 

 circulatory systems, one or both eyes defective, cyclopia. 



Alteration of the oxygen supply to the egg is a commonly used 

 method of inducing teratological development. The earlier at- 

 tempts in this direction consisted in covering the whole or 

 portions of the egg with a varnish. The original purpose of such 

 experiments seems to have been to prove the necessity of oxygen 

 for the development of the chick. If the entire egg is varnished 

 the embryo of course dies at a certain stage of development as 

 shown long ago by Dareste. If the egg is partially varnished, 

 development tends to be abnormal. Gerlach and Koch ('83) 

 varnished the entire egg except for a circle 4.5 to 6 mm. in 

 diameter immediately over the blastoderm. The general conse- 

 quence of such procedure was a dwarfing, often extensive, of the 

 embryo, due in my opinion to inhibition of the growing region of 



