INFLUENCE OF ROENTGEN RAYS UPON METABOLISM 8T3 



have also described an ionization chamber for measurement of the dosage 

 of Roentgen rays. Kronig and Friederieli have made ionization cham- 

 bers, the so-called ionto quantimeters, so small that they can be placed 

 within a cavity in close proximity to the part of the body to be rayed. 

 Such ionization chambers connected with an electroscope or an electro- 

 meter give an indication of the relative or absolute dosage of x-rays and 

 should therefore greatly facilitate a comparison of x-rays and radio- 

 active substances. 



Estimation of the activity of radioactive substances when expressed in 

 milligrams may be misleading unless it is based upon the activity of the 

 gamma radiation of the radioactive element solely, as indicated by its 

 power of ionization. This is the method adopted by the United States 

 Bureau of Standards. Unless the standardization by weight conforms 

 to the above there may be great variation due to the type of salt used, to 

 the presence or absence of water of crystallization and particularly to 

 the variable amount of impurity such as barium. The unit activity of 

 radium salt should be expressed as above indicated in milligrams of 

 radium element. The emanation or radioactive gas in equilibrium with 

 one milligram of radium element has been designated one millicurie. For 

 measuring the radioactive strength of solutions for bathing and drink- 

 ing and of air for inhalation the so-called "Mache" unit is commonly 

 used. One Mac-he unit is equivalent to one three-millionth part of a milli- 

 curie. Three thousand Mache units are equivalent to one-thousandth of 

 a milligram of radium element. One-thousandth of a milligram is equiva- 

 lent to one-millionth of a gram and is frequently designated as a micro- 

 gram. The French formerly took the radioactivity of uranium as their 

 standard. Uranium was considered as having a radioactivity of 1 and 

 pure radium 2,000,000 times as great. An activity of 500,000 frequently 

 reported in literature would represent one-fourth of pure radium and 

 three-fourths of impurity. 



In a quantitative study of the effect of radium radiations on the fer- 

 tilization membranes of Nereis limbata Redfield and Bright obtained 

 a physiological reaction to these radiations which could be measured with 

 such precision that the thickening of the membrane served as a physio- 

 logical index of the intensity of the radiation. Wood and Prime suggest 

 for an intensity unit of radium the rays emitted by 1 milligram of radium 

 element (1 millicurie of radium emanation) located at a point 1 centimeter 

 distant and they designate this as 1 milligram or millicurie centimeter. 

 Mottram and Russ consider the biological x-ray unit, which they designate 

 by the name rad, as equal to the exposure to beta and gamma rays from 

 2.75 milligrams of RaBr 2 H 2 O per square centimeter for one hour. This 

 is just sufficient to prevent the growth of a rat sarcoma and to produce an 

 erythema when applied to human skin, 



