366 



IMMUNOLOGICAL STUDIES 



cells of amphibian embryos ( Holtfreter, 1943, 1948). Experi- 

 ments along this line have since been performed by Spiegel 

 ( 1954a,b, 1955) on sponges and frog embryos. By use of antisera 

 he has been able to interfere with the reaggregation process in 

 such a way as to indicate a role of specific surface antigens. 



A striking recent example of specific interaction of cells is given 

 in the experiments by Weiss and Andres (1952) who showed 

 that presumptive melanoblasts of dissociated embryonic chick 

 cell suspensions when injected into the blood stream of early 





^ 



Fig. 3. Diagram illustrating the aggregation of vegetative amoebae 

 (A) of Dictyostelium into a pseudoplasmodium (B) and transformation of 

 the latter into the sorocarp. (From Gregg et ah, 1954.) 



chick embryos localized in the proper regions characteristic of the 

 cell type and of the donor strain. Other examples may be found 

 in experiments on type-specific reaggregation and differentiation 

 of dissociated embryonic cells in mixed cultures, as in the experi- 

 ments of Trinkaus and Groves ( 1955 ) and of Moscona ( 1956 ) on 

 mixed mesonephric and limb-bud cells of the chick embryo, and 

 of Townes and Holtfreter ( 1955 ) on mixed aggregates of am- 

 phibian gastrula and neurula cells. 



Another kind of material, the slime mold Dictyostelium, has 

 been investigated recently by J. H. Gregg (1956). In this organ- 

 ism individual amoebae aggregate to form a cell mass which un- 

 dergoes further morphogenetic change ( Fig. 3 ) . With three spe- 



