Ramsay and Soddy (_loc. cit._) have also observed the presence of helium in the gases evolved by solution of radium bromide. This important result is considered in detail in section 267. Physiological actions. =125.= Walkhoff first observed that radium rays produce burns of much the same character as those caused by Röntgen rays. Experiments in this direction have been made by Giesel, Curie and Becquerel, and others, with very similar results. There is at first a painful irritation, then inflammation sets in, which lasts from 10 to 20 days. This effect is produced by all preparations of radium, and appears to be due mainly to the α and β rays. Care has to be taken in handling radium on account of the painful inflammation set up by the rays. If a finger is held for some minutes at the base of a capsule containing a radium preparation, the skin becomes inflamed for about 15 days and then peels off. The painful feeling does not disappear for two months. Danysz[221] found that this action is mainly confined to the skin, and does not extend to the underlying tissue. Caterpillars subjected to the action of the rays lost their power of motion in several days and finally died. Radium rays have been found beneficial in certain cases of cancer. The effect is apparently similar to that produced by Röntgen rays, but the use of radium possesses the great advantage that the radiating source can be enclosed in a fine tube and introduced at the particular point at which the action of the rays is required. The rays have also been found to hinder or stop the development of microbes[222]. It would be out of place here to give an account of the numerous experiments that have been made by physicists and physiologists on the action of the rays of radium and of other radio-active substances on different organisms, such as caterpillars, mice and guinea-pigs. In some cases, the experiments have been carried out by placing the organisms in an atmosphere impregnated with the radium emanation. The effect of an exposure under such conditions for several days or weeks has been found generally harmful and in many cases fatal. The literature in this new department of study is already large and is increasing rapidly.