5S (122) Society for Experimental Biology and Medicine. 



by a number of external agents. If the eggs are revolved at the 

 rate of 180 revolutions per minute ; if they are put into salt solu- 

 tions of definite strengths ; if they are subjected to a low or to a 

 high temperature ; if they are deprived of sufficient oxygen or 

 surrounded by carbon dioxid in solution ; if they are placed on 

 wet filter paper instead of developing under water — in any of 

 these ways abnormal embryos result. 



An examination of the effects of these external agents brings 

 out two points of especial interest. First, that the effects are not 

 gradual, i. c, corresponding in degree to the increasing strength 

 of the agent employed, but that no effects appear up to a certain 

 point and then suddenly the agent begins to act. Increasing the 

 strength of the agent above this point may for a small range in- 

 crease the effect, but this occurs within extraordinarily narrow 

 limits compared with the lower range of non-action. The most 

 plausible explanation of this mode of behavior in most of the cases 

 is as follows : The agents act by coagulating certain parts of the 

 egg, thereby preventing their further development. Other parts 

 of the eggs that are made up of different colloids or of different 

 concentrations of colloids remain unaffected, and proceed to carry 

 out their development as far as the presence of the injured region 

 allows. 



The second point was the one that the author spoke of espe- 

 cially. Despite the great diversity in the form of the abnormal 

 embryos, most of them may be reduced to modifications of the 

 same type. For example, in many cases the dark cells of the 

 upper hemisphere do not grow down over the lower hemisphere 

 to produce there the embryo, but, remaining at the top of the egg, 

 partially constrict off from the yolk cells at, or even above, the 

 equator of the egg. Out of these dark cells the abnormal embryo 

 develops usually in the form of a ring. Sometimes one side only 

 of the ring develops and a half embryo appears ; sometimes only 

 the anterior end of the ring develops and an anterior embryo ap- 

 pears (often more or less " open "), etc. 



The author called especial attention to the fact that the abnor- 

 mal embryo develops in the material of the upper hemisphere ; 

 while the normal embryo develops over the lower hemisphere. 

 Two interpretations of this difference seem possible. Either the 



