1. The cells of the proximal convolutions of the rat can be filled with fine droplets by the administration of certain amino acids in non-toxic dosage.

2. These minute droplets resemble in their Gram positivity and in their phospholipid and PNA content on biochemical analysis (3) the larger droplets that form in the cells of the proximal convolution during the absorption of certain proteins.

3. The positive or negative reaction to 3 specific histochemical procedures of the fine droplets forming after administration of 7 amino acids gave such a high positive correlation with theoretical assumption as to warrant the following inferences: (a) that the methods are specific under the conditions of the experiment; (b) that the droplets contain a higher concentration of the administered amino acid than the general cytoplasm of the cells which contain them.

4. The mitochondrial rodlets of epithelium of the proximal convolution contain sulfhydryl in high concentration, a finding which correlates well with their enzymatic activity.

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