38 BACTERIA IN RELATION TO PLANT DISEASES. 



experimenting it was found that 5 grains of the clean, white guncotton per 100 

 cc. of the fluid gave a solution very satisfactory to work with. About 24 hours is 

 required to dissolve the guncotton into a homogeneous mixture, of which there 

 should be at least 800 cc. This should be stored in a cork-stoppered bottle of shape 

 convenient to hold in one hand. It is then ready for use. The clean test tube, 

 thoroughly dry on the inside, is now held in one hand in a slanting position, mouth 

 up, while with the other the collodion is poured slowly and steadily into the tube, 

 while the latter is slowly rotated. In this way air-bubbles are avoided and the entire 

 interior of the tube is moistened. When this has taken place and about an inch of 

 fluid has accumulated in the bottom of the tube, the excess is poured back into the 

 bottle, slowly rotating the slanted tube, as before, so as to cover again the entire 

 interior with as uniform a layer as possible. When the bulk has been poured back, 

 the tube is stood upright, mouth down, to drain on a sheet of clean paper. In two 

 or three minutes it will have drained sufficiently, the excess of accumulations about 

 the mouth being wiped off on the paper now and then. The tube is then seized 

 and rotated in a horizontal position for four or five minutes with the mouth in the 

 draft of an electric fan, or the rotation may be somewhat longer if no air-current 

 is available. A little experience will tell when the sack is dry enough to remove 

 from the tube. The strong smell of ether must have somewhat subsided and the 

 collodion must not feel wet around the mouth of the tube, as will be the case if the 

 layer of collodion is too thick in places. If it is taken out in this condition, the 

 thick, wet places will become clouded. The collodion is now cut free at the lips of 

 the test-tube by means of a pin-point or other sharp instrument and the tube is filled 

 with cool water, taking care to let it also flow between sack and wall of tube if there 

 is any shrinkage. In a minute or two, if the work has been well done, the sack, free 

 from air-bubbles and filled with water, may be readily lifted out of the tube. It is 

 then placed in a jar of water, where it remains until it is ready to receive the sub- 

 stance to be dialyzed. These sacks are quite tough, and there is little danger of 

 tearing them during filling and tying. 



When the silicate jelly or other substance has been placed in them, the mouth 

 is brought together and tied by means of a small rubber band, the elasticity of which 

 keeps the sacks perfectly tight. Silicate jelly should be dialyzed for at least 12 hours, 

 and sometimes for 24 hours, if ever)' trace of salt must be removed. The writer 

 fills the sacks with the silicate jelly in the afternoon and leaves them in running tap 

 water over night. The next morning they are taken out, their contents emptied 

 into a clean beaker, the nutrient salts added, and the fluid immediately pipetted into 

 tubes, flasks, etc., and sterilized by heat. The nutrient substances should be dis- 

 solved in advance, so as not to delay the preparation of the medium. They should 

 be added for this purpose to a minimum quantity of water. Some dissolve slowly, 

 and there is a preferable order of solution, the glycerin being added last in case of 

 Fermi's solution. 



For the preparation of silicate jelly a Beauine" hydrometer for liquids heavier 

 than water is used. C.P. hydrochloric acid of any specific gravity is diluted with 

 distilled water until it tests 1.10 011 the scale of the hvdrometer when cooled 



