DRS. HILGARTNER AND NORTHRUP EXPERIMENTS WITH X-RAYS. 31 
suggestion arising, possibly, from one or more of three causes: the ques- 
tion put to the subject, the heat sent out from the tube, or the sound 
produced by the discharge of the coil. A screen of any kind placed be- 
tween the tube and the subject's face could in all cases be detected. Mr. 
D., the University student, thought, however, that the presence of the 
screen was known to him by the sound or heat shadow which it cast upon 
the face. It is well known that the blind can detect the presence of 
boards and other objects placed several feet in front of them by the sense 
of hearing, sounds passing from the subject to the object and back again 
by reflection probably constituting the means by which the presence of 
the object is known. The next step was to plac§ an ordinary drafting 
board, three-fourths of an inch thick, between the subject and the tube. 
The X-rays passed freely through this board, as was proved by the aid of 
the fluoroscope. While the X-rays were streaming directly into the eyes, 
a sheet of lead, impervious to the rays, was repeatedly placed between the 
tube and the drawing board, and then removed. Xo sensation was pro- 
duced upon the eyes of any of the blind or upon the normal eyes by 
means of which the persons could detect when the lead sheet was screen- 
ing the rays from their eyes and when it was not. This experiment was 
tried repeatedly with normal eyes, with those having some light percep- 
tion, and with those who had none. The authors are, therefore, forced 
to conclude that the X-rays themselves have no power whatever of ex- 
citing vision, or even light perception, in any kind of an eye, diseased or 
normal. Of course, these results regarding the blind apply only to the 
eleven subjects experimented upon, and it would be unscientific to say 
that no subject can ever be found in whom the X-rays will excite light 
sensations. Xone of the blind subjects could see anything by looking into 
the fluoroscope, even those having some light perception getting no sen- 
sation, and our experiments gave us no hint that X-rays, or any other 
kind of rays, proceeding from the Crooke's tube are able to give any light 
perception to those who are blind from any cause whatever. 
Even though others may think they find that the X-rays may, in some 
subjects, excite light sensation, the X-rays can serve no useful purpose to 
the blind. The X-rays not being refracted, they never give images of ob- 
jects, and if the blind persons should be found whose retinas may be ex- 
cited by them they would only distinguish different degrees of homo- 
geneous brightness. It is not impossible that X-rays falling on a diseased 
retina might exert, by repeated application, a curative influence, though 
there is no reason supported by facts to encourage such a belief. To our 
minds, it is highly absurd to suppose that the X-rays can stimulate a dis- 
eased or destroyed eye to light sensation when they have absolutely no 
effect upon a normal eye. We should not have thought the above nega- 
tive results worthy of record if the matter had not been taken up by 
scientists of eminence, and the newspapers filled with trashy and mis- 
leading myths. 
