666 POPULAR SCIENCE MONTHLY. 



graph of an elbow joint whicli shows the texture of the bones 

 (Fig. 5).* 



The use of the fluorescent screen, too, has been greatly ex- 

 tended. Dr. Francis H. Williams, of Boston, has used it as a valu- 

 able instrument in medical diagnosis, especially in studying lung 

 diseases. It has been used at the Harvard Medical School to fol- 

 low the processes of digestion. To accomplish this, in one instance 

 a goose was fed with food mixed with subnitrate of bismuth, a 

 salt which absorbs X rays. 



The passage of the dark mass down the long neck of the bird 

 could be traced on the fluorescent screen, and the peculiarities of 

 its motion in tlie erullct could be studied. A cat was also fed with 



Fig. 5. — Plioto^niph of an (.'lliow joint. sJiowing the texture of the hones 



the same substance, and the movements of its stomach noted. 

 These movements were analogous to those of the heart — in other 

 words, were rhythmical when the processes of digestion were going 

 on normally and uninterruptedly. When, however, the cat was 

 irritated, it may be by the sight of a dog, these pulsations instantly 

 ceased. As soon as the source of vexation was removed and the 

 purring of the animal showed a contented frame of mind, the 

 stomach resumed its rhythmical movements. The dependence of 

 the digestive apparatus on the state of the nervous system was thus 

 clearly shown. The fomnle cat was much more tractable under 

 these experiments than the male. 



The use of the X rays is accompanied with some danger if the 

 Crooke's tube is not properly used. A long exposure to the X rays 

 is apt to produce bad burns which are like sunburns, and lead in 

 certain cases to bad ulcerations. They are long in healing and are 

 characterized by a peculiar red glow, especially on exposure to a 

 cold wind. To prevent them one should place a sheet of thin 

 aluminum between the Crooke's tube and the part of the body 



* Tiiken bv Professor Goodspeecl, University of Pennsylvania. 



