1602 Journal of Applied Microscopy 



require much care, skill, and intelligence, to select the proper pieces and put 

 them together with such nicety that the shell is but a single layer thick, and yet 

 no gaps are left. 



But the drop of chloroform is not to be outdone, and under the proper condi- 

 tions will produce a shell not inferior to that of Difflugia. This may be shown 

 very simply. Chloroform is rubbed up with fragments of glass in a mortar until 

 the glass is reduced to the finest dust. Then with a pipette drawn out to 

 a small point drops of this mixture of chloroform and glass dust are injected into 

 water. At once the grains of glass come to the surface of the drops so formed 

 and arrange themselves there in a single layer, without chinks or crevices, exactly 

 as in the shell of Difflugia. The chloroform drop is covered with a shell of a 

 delicacy and beauty equal to that of Difflugia, and almost indistinguishable in 

 texture from it. Some of these artificial shells, if unexpectedly found with the 

 microscope, would certainly be taken for those of Difflugia. 



In place of chloroform, linseed oil or other oils may be used. They must 

 then be injected into 70 per cent, alcohol, since the oil would float upon water. 

 The process is exactly the same as when chloroform is used. 



These experiments are likewise due to Rhumbler, who has so much extended 

 our knowledge of the part played by physical laws in the activities of the lower 

 organisms. 



Demonstration with the Projection Apparatus. The experiments described 

 above may be shown to individual students, or groups of students, or even per- 

 haps performed by the students, if time permits. But the most satisfactory way 

 of showing them to a large class is by projection on the screen. If a good ster- 

 eopticon, employing the arc light, is available, this can usually be done in a 

 satisfactory manner without other unusual apparatus. In the accounts usually 

 given of projection with the microscope, much supplementary apparatus is 

 described, which is unquestionably useful, but not necessary, so that the reader 

 is likely to get the impression that projection with the microscope cannot be done 

 without a complicated and expensive outfit. With a ^<7<?</ stereopticon employing 

 the arc light, a dish with parallel sides, full of water, to cut out the heat before 

 the light strikes the concave mirror of the microscope to pass up through the 

 lenses, any good microscope having low powers, and a mirror to place above 

 the microscope, so as to reflect the images onto the screen, very satisfactory pro- 

 jection is possible. All the experiments described above may thus be shown to 

 a large class, except the making of the " artificial Difflugia shells." The artificial 

 shells may be shown on the screen after they are made, but even this is not very 

 satisfactory, as the bits of glass of which the shell is made intercept so much 

 light that the image of the shells on a screen is little more than a dark spot. 

 University of Michigan. H. S. JENNINGS. 



