990 BIOLOGICAL EFFECTS OF RADIATION 



of the effect of the thickness or material of the wall of the container. 

 In other words, precise quantitative work was impossible. Technique 

 had also not been perfected for dijfferential tests of the three different 

 types of rays — alpha, beta, and gamma. 



Guilleminot had recognized this need in 1907, and proposed as a 

 unit of intensity (M) of the field of irradiation the quadruple of the 

 intensity producing the same luminescence as a standard of 0.02 gm. of 

 radium bromide of 500,000 activity,^ spread over a circular surface of 

 1 cm. in diameter, and placed at a distance of 2 cm. from the phosphores- 

 cent surface. Then the unit of quantity of radiation will be the quantity 

 acting for 1 min. when the field has one unit of intensity. Investigations, 

 however, were carried on from 1908 to 1916 with and without (mostly 

 without) reference to this unit. 



In 1905, Dr. H. Mache, of Vienna, studied the radioactivity of springs 

 and ri\-ers of Bohemia and Austria. This radioactivity, of course, is very 

 weak, and Mache proposed and defined a mass unit of the concentration of 

 the emanation found in springs, etc. If the quantity of emanation found 

 in one liter of the water tested is passed through an electroscope and the 

 radiation given off can maintain a saturation stream of 1 X 10~' elec- 

 trostatic units, then the water has an emanation content of one Mache 

 unit (1 ME). 1 ME = 3.64 X lO-^" curie/liter. There was later 

 proposed for the concentration of emanation the unit, 1 "Eman" 

 (= 10-10 curie/liter). 



In 1910 the International Congress for Radiology and Electricity, 

 Brussels, proposed as the unit of radium emanation the amount of 

 emanation in an enclosed container which is in equilibrium with 1 gm. of 

 metallic radium. This unit was called a airie after M. Curie, who was the 

 first to devise a quantitative method of measuring the emanation. One 

 Mache unit = 4 X lO'"^'' curie or 4 X 10"^ millicurie. A millicurie and a 

 microcurie are the quantities corresponding respectively to 1 mg. and 

 0.001 mg. 



Since the paper of Gager (26) is readily available, it is not essential 

 here to review the literature of that period in detail. Because of its 

 bearing on the subject of photosynthesis, mention should be made, 

 however, of the work of Stoklasa, Sebor, and Zdobnick^ (84) in 1911 and 

 1913, who reported that "under the influence of the emanation of radium, 

 hydrogen, and carbonic acid, in the presence of potassium bicarbonate, 

 react to form formic aldehyde which, on contact with potassium, polymer- 

 izes and gives reducing sugars" (see 84, page 648). Whether or not 

 radioactivity is involved as an essential factor in the normal process of 

 photosynthesis has never been demonstrated. 



In the earlier work it was determined that embryonic tissue {e.g., 

 cambium) is more sensitive to the rays than mature differentiated tissue, 



^ That is, in terms of an oqual weight of uranium. 



