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Special importance should be attached to Brachet's induction experiments with the pellet prepared by ultracentrifugation from the amphibian gastrulae referred to under (ii) above. That the RNA content
of the sample was much lower than that of the sample used in our
experiment may be due to a difference in preparation technique. In
FIG. 1 3 . T h e microsome fraction of Triturus neurulae. A n electron micrograph of a
thin section prepared b y Karasaki. Micro-particles and cytoplasmic vesicles are indicated,
χ 40,000.
view of the fact that the sample was tested after ethanol treatment, and
no efforts were made to distinguish the regional type of induction
obtained by insertion experiment, it is rather difficult to judge the value
of the neural induction registered in 13 cases out of 35 experiments as
evidence for the inductive activity of the microsome fraction in the
normal organizer action. Nevertheless, Brachet's conclusion, drawn
from the experiments, that cytoplasmic granules rich in R N A may be
responsible for the organizer action, appears to be justified by our
present preliminary results.