1. When it was added to the photographic emulsion at the beginning of the after-ripening, penicillin retarded the chemical ripening. And its degree was emphasized by various methods of decomposition.
2. It was concluded that the origin of the retarding action was lied in the decomposition products of penicillin.
3. In the decomposition products, penicilloic acid, penillic acid, penaldic acid and penillo-aldehyde are expected to be the retarding substance, and penicillamine to be the fogging agent.
We wish to express our appreciation of the many valuable suggestions given by Mr. Shin Fujisawa, the head of Research Institute, Fuji Photo Film Co., and our thanks to Prof. E. Ochiai and Mr. Y. Kashida, Tokyo University, about offering the valuable samples of thiazolidine derivatives.

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