Contribution to the problem of neurogenic potency in post-nodal isolates from chick blastoderms
✍ Scribed by Rudnick, Dorothea
- Publisher
- John Wiley and Sons
- Year
- 1938
- Tongue
- English
- Weight
- 786 KB
- Volume
- 78
- Category
- Article
- ISSN
- 0022-104X
No coin nor oath required. For personal study only.
✦ Synopsis
When in 1931 and 1932 Hunt reported that he was unable to obtain differentiation of central nervous tissue in chorioallantoic grafts from portions of the definitive streak chick blastoderm cut farther than 0.21 mm. behind the primitive pit, he raised, it would appear, a controversial issue. Hunt's negative results are based on a large number of cases ; nevertheless, in view of the variability of the graft response as a measure of differentiation capacity, it is perhaps not too surprising that other workers should obtain other results. Dalton ( '35) reports a considerable number of cases of nerve cord tissue (three out of fourteen) in grafts made of a region comprising, one judges from his diagrams, the posterior threefifths of the primitive streak in blastoderms of 16 to 24 hours' incubation. He does not make clear just what morphological stages these individual cases belong to or furnish specific measurements ; nevertheless the difference between his results and those of Hunt are too wide to be reconciled at present. I may say that I have examined a number (twenty-three) of my own grafts of posterior pieces of the definitive primitive streak blastoderm, comparable to Hunt's material. Of these, seven had been cut 0.2 mm. or less posterior to the pit, and six contained central nervous tissue. Of the remaining sixteen, all cut more than 0.2 mm. behind the pit, none contained masses of nerve tissue-a few ganglion cells only were observed. These findings are in complete accord with those of 369