and other Salts on Gelatin. 259 



dioxide in order to clarify and bleach it, therefore it seemed 

 likely that the so-called growth originated about a precipitate 

 of an insoluble sulphate, and this idea was substantiated by the 

 circumstance that only those metals which form insoluble sul- 

 phates could produce the growth. 



The formation of a cell round a particle of precipitate may be 

 explained by an alteration in the degree of hydration either of 

 the precipitate or of the surrounding gelatin, thus forming an 

 empty space. It has been stated by Mr Burke that the cells 

 disappear on heating. This of course would naturally be the 

 case as the gelatin would melt and the vacuole collapse, and the 

 small particle of precipitates might easily escape notice. 



Experiments were made with the object of ascertaining whether 

 the gelatin could be rendered truly " sterile " to the action of 

 radium salts. • It was found that on adding a solution of either 

 radium or barium salt to liquefied gelatin a precipitate was 

 obtained, which varied in amount with different samples of 

 gelatin. This precipitate was filtered off and was found to 

 consist of barium sulphate in both cases. A clear liquid was 

 secured by filtering through a porous tube under pressure. Drops 

 of this liquid were allowed to set on glass slips, a speck of radium 

 added, and the preparation watched under the microscope. No 

 growth could be seen. This was to be expected, for the matter 

 forming the precipitate having been removed the growth natur- 

 ally could not form. On adding to this sterile gelatin a small 

 quantity of a soluble sulphate, and testing with radium, the 

 growth made its appearance. Solutions of other gelatinous and 

 mucilaginous substances were used, such as sodium silicate, col- 

 loidal calcium sulphate, starch, gum, etc. With sodium silicate 

 and calcium sulphate, growths made their appearance, but this 

 was not the case with starch or gum unless a small amount of 

 soluble sulphate was present. If the solutions were made with 

 tap water instead of distilled water, the sulphate present in the 

 former was quite sufficient to cause a very perceptible growth. 



From these experiments it seems quite conclusive that radium 

 has no specific action upon gelatin such as to lead to the for- 

 mation of cells, and that any effect which may be seen is due 

 to the barium, which makes up the greater part of the radium 

 salt, acting upon the sulphur compounds present in the gelatin. 



18—2 



