1892.] THE MICEOSCOPE. 207 



tion of water from it. The inoculation surface becomes irregu- 

 larly concave, the thin end becomes dry, and curls, and the prep- 

 aration presents an unsightly appearance. 



When the potato cultures are to be used for exhibition pur- 

 poses, it is desirable to have them present a neat appearance. 

 The aim of the writer is to describe an apparatus which he has 

 devised to prevent the changes in form referred to. 



The apparatus consists of two pieces : a plugger, represented 

 by figure i, and a curved knife, represented by figure 2. 



The plugger is made from a metal tube about six inches long, 

 and of a diameter a little less than the culture-tubes to be used. 

 The side of the metal tube is cut out by sawing slantingly through 

 the wall and across the inner diameter of the tube to the opposite 

 wall at such an angle that the distance traversed by the saw will 

 be about two inches, and then by sawing vertically across the 

 diameter of the tube to the wall of the opposite side. The end of 

 the tube nearest the side opening is sharpened from the outer sur- 

 face, and a wooden handle is fitted into the other end. 



The curved knife (fig. 3) is used to cut a convex surface on 

 the potato section so as to compensate for the loss by shrinkage 

 from evaporation. After a time this convex surface will become 

 nearly flat, whereas, if the surface were cut flat at the outset, it 

 w^ould now be irregularly concave. 



This knife is made by cutting out a segment of a circular tube 

 of about one and one-half inches in diameter, the segment having 

 continuous w^ith it a narrow portion of the wall of the same tube, 

 which portion serves as a handle. The segmental portion is 

 sharpened upon its convex surface. 



When it is desired to make a potato preparation, both ends of 

 a large potato are cut oft', and the plugger is passed through it by 

 a rotary vertical movement. The potato c^'lmder, wdiich appears 

 in the plugger, should be long enough to reach a short distance 

 into the hollow handle, so that it will be held firmly. By pass- 

 ing the curved knife into the potato cylinder and across its diame- 

 ter in contact with the sides of the opening in the plugger, the 

 cylinder is divided. The outer piece of the divided cylinder will 

 fall out, and the piece which remains in the plugger now has a 

 beveled surface for inoculation, and it can be removed by pushing 

 it up a short distance into the hollow handle of the plugger. 



The thin end of the section should be trimmed oft' for the dis- 

 tance of about half an inch to prevent its curling, and a notch 

 should be made in the side of the end of the cylindrical portion of 

 the section to admit the passage of moisture from the water res- 

 ervoir of the culture-tube to the potato chamber above it. 



Figure 3 represents the potato section placed in a reservoir-tube 

 ready for use. — From the American Monthly Microscopical 

 Journal iox October. 1892. 



