348 IMMUNOLOGICAL STUDIES 



protein against which they were originally produced but rather 

 certain determinant groups. Thus statements as to the time of 

 detection of various proteins during development must be quali- 

 fied to the effect that the substance is not necessarily chemically 

 the same as that in the adult, since the antisera identify only cer- 

 tain parts of the molecule. The cited experiments on the serum 

 proteins of the chick show that the determinant groups of serum 

 albumin are present in sufficient quantity to be detected, by the 

 absorbed antisera employed, at about the fifth day of incubation; 

 those of a,/3-globulin at about the sixth day, and those of -/-globu- 

 lin at the ninth to twelfth day. 



The only other detailed immuno-embryological experiments 

 with highly purified proteins that have been so far reported are 

 those of Ebert (1953, 1955) on myosin and actin. By the use of 

 antisera made specific for cardiac myosin by absorption with skel- 

 etal myosin he has detected determinant groups of cardiac myo- 

 sin in chick blastoderms in the mid-primitive streak stage, but 

 not earlier. Tests with various portions of the blastoderm at vari- 

 ous stages indicated that the determinant groups are detected 

 throughout the blastoderm (perhaps confined to the epiblast) at 

 the mid-streak stage, but become restricted in the head process 

 and head fold stages to two lateral areas corresponding roughly 

 to the location of potential heart-forming areas (Rawles, 1943). 

 The determinant groups of cardiac actin ( or at least one antigenic 

 component thereof ) were first detected in the head-process stage, 

 with localization similar to that of the myosin. 



There is, then, evidence that at least the determinant groups 

 of certain proteins ( if not the proteins themselves ) characteristic 

 of adult tissues or organs appear in detectable amounts prior to 

 difl^erentiation of the particular tissue or organ, and that their 

 distribution may coincide with the corresponding "organ-form- 

 ing" areas of the early embryo. This suggests possible causal con- 

 nection with processes of determination and diff^erentiation of 

 various organs and tissues in the embryo, since the general fea- 

 tures of the results obtained with lens, heart, serum proteins, etc., 

 can be assumed to be representative of what may be found for 

 other tissues and organs. 



