June 4, 1897.] 



SCIENCE. 



859 



more certain and accurate, and less liable 

 to get out of order than the foreign form. 

 The Zimmerman microtomes are of a very- 

 high grade of workmanship, and I can 

 recommend them with confidence, having 

 thoroughly tested them. The Cogit micro- 

 tome also appeared to me thoroughly good, 

 but I have had no opportunity to test one 

 by prolonged use. Zimmerman has added 

 to the mici'otome, as made by him, an at- 

 tachment to give a feed of 0.001 mm., but 



BUjjIiilS 



The automatic wheel microtome will 

 cause only vexation and disappointment if 

 it does not receive the utmost care. I will, 

 therefore, mention the most necessary pre- 

 cautions. The following are of the first 

 importance : 



1. Keep the microtome perfectly clean To 

 accomplish this, not only must all dust be 

 removed, but also no oil which has become 

 thick or gummy must be allowed to re- 

 main. A special risk comes from the paraf- 



it seems to me that the addition is of slight 

 value, since the accuracy of the instrument 

 cannot be carried so far, because with ver- 

 tical ways the precision of movement cannot 

 be made so great. No doubt such sections 

 (of 0.001 mm.) can be made with the ma- 

 chine, but if the object offers any difliculty 

 from its size or its hardness the machine 

 will fail. For very fine work another type 

 of microtome is called for. 



fine, small bits of which are very apt to fall 

 upon the instrument, and if they ai'e per- 

 mitted to lodge on anj' of the movable parts 

 they majr easily cause serious injury and 

 will certainly prevent even section-cutting. 

 Extreme cleanliness is indispensable, and 

 to better secure it the microtome should 

 always be covered when not in actual use. 

 2. Keep the microtome perfectly oiled. All 

 the movable parts must be well lubricated 



