134 THE AMERICAN MONTHLY [May 



improved pattern of their well-known rocking microtome. 

 The earlier instrument was introdued as far back as 1885, 

 and has made its way into colleges and laboratories 

 throughout the world. It is undoubtedly the simplest, 

 cheapest, and most efficient microtome for the cutting of 

 serial sections. The improvements introduced in the new 

 model are increased rigidity, impossibility of making sec- 

 tions in the upward movement, or of cutting thick and 

 thin sections, graduated arc for showing the thickness of 

 the sections, catch for holding the object above the razor 

 edge, improved method of fixing the cord, and new ob- 

 ject holder. The first three of these improvements ap- 

 pear to us to be the most important, and to have been suc- 

 cessfully accomplished. The price of the microtome is 

 slightly higher than hitherto, being about $24, without 

 razor and object-holder. There is one drawback to the use 

 of a microtome of this type, and that is that the cut sur- 

 faces have necessarily a slight curve on them. In most 

 cases this may be ignored, but it is as well to mention here 

 that another pattern is made by the same firm, at a rather 

 higher price, by which entirely flat sections are cut. Be- 

 ginners may perhaps be reminded that a rocking micro- 

 tome is useful mainly for cutting long "ribbons" of sec- 

 tions such as are used in biological and other laboratories. 

 Light. — The cone of light transmitted by the conden- 

 ser should approximate to that of the objective ; but few 

 objectives will stand solid cones of light equal to their ap- 

 ertures. If the worker is using the Abbe illuminator of 

 1-2 N. A., he will of course, only obtain a total aperture 

 of 1 N. A., unless the condenser is in immersion contact 

 with the under side of the slide. Theoretically, therefore, 

 this condenser is suitable for lenses of 1 N. A., and even 

 more, and suitable also for lenses of lower apertures by 

 the simple process of stopping the aperture down by the 

 means of the iris or other diaphragm. The worker soon 

 becomes expert in the use of the iris diaphragm ; but we 



