Abstract
1) The author was able to demonstrate a nucleolar substance in mammalian nerve cells (spinal cord of rat, mouse, guinea pig, rabbit, dog and man) with his modification of the diphenylthiocarbazide (dithizide) method which had been introduced by Okamoto et al. (1942,1951).
2) By means of polarographican alysis of spinal cord, the author identified the dithizide positive substance with zinc. He consid e red that the substance may represent a protein-bound zinc.
3) At the post-natal stage (the 21,28 and 42 days a f ter birth), the dithizide positive substance appears not only in nucleolus, but also in nucleus and in cytoplasm. From several histochemical exami nations the nucleolar positive substance seems to differ from the cytoplasmic one.
Such diffe rence might be depend on the zinc-bound protein between the two. This observation seems to support Caspersson's theory (1950).
4) From the microscopic observations it was expected that the metal increases as the animal grows, but from the polarogram of the growing spinal cord of rat it was clear that the zinc concentration decreased with animal growth.
