126 BACTERIAL DISEASES OF PLANTS 



oz., hypo. 32 oz.), slowly stirring in, with a glass rod one tumbler 

 of the green fluid (water 32 oz., dry sodium sulphite 3 oz., c.p. 

 sulphuric acid }/ 2 oz., powdered chrome alum 2 oz., dissolved 

 in the order named). 



Lumiere Plates. Consult a booklet on " Color Photography 

 With Autochrom Plates." R. J. Fitzsimons, 75 Fifth Avenue, 

 New York, Agents for Lumiere Jougla Products. 



Planars. The use of planar lenses has greatly simplified 

 the work of the pathologist. By means of magnifications rang- 

 ing from X 5 to X 25 they enable him to show every detail of a 

 surface not too irregular, and the whole of sections much too 

 large for the ordinary microscope. I make most use of mag- 

 nifications ranging from X5 to X15 and prize these lenses 

 very highly. Their only defect, if such it be, is that the field 

 must be quite flat, if the image is to be uniformly sharp. There 

 is, however, a little penetration and to make the most of this 

 we usually focus with the diaphragm wide open and then stop 

 down as much as possible. The final focusing should be on 

 clear glass, using a hand lens magnifying about X6. What 

 can be done with such lenses is shown in some of the illustra- 

 tions in this book. Figure 72 was one of the hardest to make 

 because the section is thin and now shows scarcely any stain 

 except in the bacterial masses, and because it was made on the 

 upright camera without a color screen. 



Drawings. At one time the pendulum of scientific senti- 

 ment swung away from drawings toward photographs, because 

 it was said the drawing represents only the ideas of the artist 

 whereas the photograph cannot lie, but now it has come back 

 again, since it has been recognized that the latter statement is 

 not strictly true (Fig. 2106, c), and that the former objection 

 lies chiefly against artists who are not naturalists. 



For many purposes, a good drawing is better than a good 

 photograph, but there is no reason why the scientific man should 

 not use both. I have heard many students say: "I can never 

 learn to draw," but with few exceptions such is not the case. 

 Every student should be encouraged to use pen and pencil 

 every day to illustrate what he sees. The more he does it under 

 proper guidance the more he will see. Certainly he has not 



