PROCESS FOR PRESERVING PEARL-OYSTER FISHERIES. 309 
When pearl oysters are the objects examined, the pearls will clearly appear in 
the radiograph, as they obstruct the passage of the rays to a greater extent than 
other portions of the oysters. I also use in connection with the tray or conveyer 
a means for identifying the particular group of objects which have been radio- 
graphed so that the radiograph may be afterwards compared with the objects 
on the tray and their 
identity established. With 
pearl oysters, those that 
have pearls may thus be 
identified, and the position 
and size of the pearls be 
ascertained, without de- 
stroying the oysters. 
The essentials of the 
tray bottom or conveyer 
are two: (1) That the ma- 
terial be composed of a 
substance which renders lit- 
tle or no resistance to the 
passage of the X rays, 
Réntgen rays, or any other 
rays penetrating matter 
opaque to light, and allows 
them to affect the sensitized medium practically as though it had not been 
interposed; and (2) that the tray bottom be as thin as possible, in order that the 
matter when held on it be but little further away from the sensitized medium 
when on the tray than when placed directly on the sensitized medium, so that 
as good definition as possible may be obtained. 
The tray may be of any shape or size desired, and may be constructed of 
cork, fiber, wood, fabric, 
aluminum, celluloid, vul- 
canized rubber, or any 
other material the qualities 
of which, as outlined above, 
are such as to afford the 
least amount of resistance 
to the rays. ‘That wet ob- 
jects may be examined without warping or distortion of the tray, I propose 
that a tray be made with the bottom of canvas, duck, or other such fabric. 
Such a receptacle is shown in the attached drawings, of which figure 1 is a 
plan and figure 2a longitudinal section. It consists of a rigid frame (a) made 
of strips of metal, wood, or other suitable material, and having hooks or pins (6) 
Fic, 1.—Plan of tray to contain pearl oysters for radiographing. 
Fic. 2.—Longitudinal section of tray shown in figure 1. 
