Abstract
In order to find to the numerical value of the density of the chest X-ray photograph, which is suited for the diagnosis, the density of 143 seats of photograph selected for the X-ray contest was measured : and the average density of every part of the film, the average maximum density of every year, the standard deviation and the relation between the conditions of photographing and the density were studied. The results were as follow : 1) The average density of the chest was 1.5-1.6 and there was little difference in the density. 2) The mutual relation between the conditions of photographing and the density did not clearly appeared, which is considered to be because of the diversity of the apparatuses.
