PREVIOUS INVESTIGATIONS UPON ANIMALS 45 



says, as to produce parthenogenesis. This last result has not been 

 confirmed. 



Danysz ^^' ^^ found the tissues in the peritoneal cavities of guinea 

 pigs less sensitive than the skin, but the central nervous system in- 

 finitely more sensitive. One centigram of radium in a sealed glass 

 tube, placed above the backbone and part of the cranium of a mouse 

 one month old, produced phenomena of ataxia and paresis in about 

 three hours. Tetanus convulsions followed in from seven to eight 

 hours, and, if the tube was left in place, death ensued in twelve to 

 eighteen hours. The older the mouse, the less sensitive he was to 

 such exposure. At the age of three to four months death did not 

 result for from three to four days, and at the age of one year not 

 until from six to ten days. Danysz attributed the increased resist- 

 ance to the transformation of the walls of the neural cavity from 

 cartilage to bone. Caterpillars of Ephertta are paralyzed by the ema- 

 nation, and anthrax germs cease developing after an exposure of 24 

 hours in an atmosphere charged with the emanation. The microbes 

 which produce the proteolytic enzymes of autodigestion are specially 

 sensitive. In his later paper he ^^ states that the epithelial tissues 

 of young animals are more sensitive than those of adults. 



A. Exner^^ found that blood, hair, nails, and muscle fiber, and 

 especially the crystalline lens, are made phosphorescent by the rays, 

 and Hardy and Anderson ^^ concluded that the sense organs of higher 

 animals are not at all affected by them. The sensation of diffused 

 light, caused by bringing a few milligrams of a radium salt near the 

 head is purely of retinal origin, and not due to a response of the 

 optic nerve or brain. The tissues of the eyeball give out this diffused 

 light under the influence of the/9 and y rays. Fresh lenses of sheep, 

 ox, and rabbit, and also skin, fat, and muscle are made to glow when 

 exposed to the rays. The eyelids are extremely opaque to radium 

 rays, and this possesses added interest in view of the fact that a 

 penetrating radiation exists in the air (p. 25). Exner's observations 

 were confirmed in 1904 by Bouchard, Curie and Balthazard.^^ In the 

 same year S. Exner,^^ exposing the tails of mice, determined that 

 the /? and y rays are both physiologically active, the former less so 

 than the latter. 



According to Perthes, ^^ an intensity of X rays not sufficient to kill 

 the cells of man and the chick, greatly retard cell-division. The 

 rays similarly affected the cells of Ascaris. 



