482 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



genesis, for the explanation of which Lacroix (1946, 1951) has suggested the exist- 

 ence of a substance which he has called osteogenin^ . More recently, Danis (1957) 

 has carefully studied the production of a bone shell by pieces of bone marrow 

 grafted into the anterior chamber of the eye, A positive result always occurs 

 with autotransplants, frequently with homotransplants, and never with hetero- 

 transplants. His experiments included grafts of killed bone marrow, which proved 

 ineffective and the author felt entitled to doubt the existence of osteogenin. From 

 the standpoint of an embryologist, however, this objection does not seem too 

 valid. The embryologist emphasizes that bone marrow is a powerful xeno-inductor 

 and he observes that during the first five days, the ocular graft goes through a 

 process of partial cytolytic decay and dedifferentiation to become a blastema-like 

 mass; this rapidly redifferentiates into osteogenic areas mixed with hematopoietic 

 marrow and finally reorganizes into a peripheral bone sheath containing a core 

 of marrow. Clearly, bone is produced by the implant and not by the host tissue 

 which would function as a reactor. Reciprocally, it is known that grafts of repar- 

 ative fibrocartilage can develop into a small bone containing marrow. Thus, 

 bone and marrow form a morphogenetic system; when one of the components 

 is excluded, the other reorganizes to privide the complementary structure. One 

 may infer that this process is quite analogous to the reorganization of an or- 

 ganizer fragment, or to the regeneration of a lens from the retina. We also have some 

 reason to suspect that such processes are concerned with liberation, displacement, 

 transfer and other activities of organizins. 



In the majority of cases, true growth only takes place after the establishment of 

 differentiation, since most germinal systems possess reserves, which need only to 

 be converted into active protoplasm. However, embryonic cells are capable of 

 assimilation at earlier stages, as is clearly apparent in mammals. 



All mechanisms disclosed by the study of development are more or less correlated 

 with specific growth processes, and this is particularly true for organizins. Students 

 of normal and pathological growth should be aware that the organisms possess, 

 at the beginning of their development, powerful growth devices which may well 

 have some still-unknown equivalent in adult cells. 



^ The existence of an osteogenic factor in rabbit bones is supported by recent studies of 

 Moss (1958). 



