E. Weinig, O. Mezger, H. Rall, and W. Heess, utilizing the diffusing nature of chloride contained in ink, judged the degree of papers. They also applied their above method to the judgment of the degree of oldness of bloodstain that, sticks to paper and cloth. The writer not only examined the above result of theirs but also improved it a little and then applied his improved method to the revealing of latent fingerprint that sticks to paper and wood. The result is conclude as follows: 1. The chloride contained in the bloodstain, spermstain, and spittlestain, that stick to paper and wood, regularly widen from the circumference of the stains as time elapses, when it is left alone in a room except in so far as humanity is extremely high there, and therefore you can judge the degree of oldness of the stain by measuring the width of the diffusion after revealing it by means of chloridereaction in which the stain is submerged in silver-nitrate solution and then reduced with formalin to silver. It is considered that this method is a far better one than the old one of judging the degree of oldness of the bloodstain by the color and the liquescent degree of the stain. 2 The writer obtained a good result by applying the above chloridereaction to the latent fingerprint that sticks to paper and wood. That is, all the materials thet can be used in the old silver-nitrate method can be utilized in our method and the fingerprint that has once been revealed will not change, and so it need not be photographed or transforred into gelatin-paper, but can be conveniently sent in as a piece of evidence at court. Besides, the method can be applied both at day and night. It can be performed in as short a time as from 4 to 5 minutes. But the method is as efficacious only within two or three days of the sticking of the fingerprint as the other silvernitrate method is. If yuo manage to keep a finger-printed thing in a desiccator within two or three days of the sticking of fingerprint, you can always apply this method for the revaling of fingerprint.