1320 Journal of Applied Microscopy 



during each ordinary excursion of the carriage. The third defect has been met 

 by the addition of the split-nut ; it is only necessary to press upon the levers 

 which open the nut, in order to allow the object holder to sink gently to a 

 lower level. Other minor improvements have been made, of which I will men- 

 tion only the spring-buffers, which prevent the carriage, if it be moved a little too 

 far or fast, from hitting too violently against the frame of the microtome. 

 The other improvements have been intended chiefly to increase the rigidity of 

 the apparatus. 



The two instruments, above described, seem to me better suited to meet 

 the severer requirements of microtomic work, than any others which I have 

 hitherto tested. The " Wheel" microtome will probably be more used than the 

 " Precision,'' partly because it works more rapidly. It is, however, adapted only 

 to paraffin cutting. When, on the other hand, the finest grade of section work 

 and a larger variety of imbedding substances are demanded, the precision micro- 

 tome is preferable, since it can furnish not only the finest but also the thickest 

 sections, and will give perfect sections of objects which cannot be cut satis- 

 factorily with any other microtome, and, finally, it can be used for either dry par- 

 affin or wet celloidin sectioning. We consider the precision microtome so 

 much more accurate than any other, that we use it almost exclusively for cut- 

 ting the series for the permanent collection of the Harvard Embryological 

 Laboratory. Charles S. Minot, LL. D. 



New Freezing Microtome for Use with Carbon-Dioxide Tanks. 



A freezing microtome offers two great advantages to the student of micro- 

 scopic anatomy. By its use thin sections of animal tissues can be prepared more 

 quickly and in many respects in a less altered condition than is possible by other 

 methods. Freezing was one of the earliest methods discovered of rendering 

 animal tissues hard enough to be cut readily into thin slices. Thus, Stilling, in 

 1843, was enabled to prepare thin sections of the central nervous system. Since 

 that date freezing, as a method of hardening, has always, to a greater or less extent, 

 been utilized by histologists. 



In the earlier days, freezing mixtures were made use of. The stand on which 

 the object to be cut was placed was surrounded by ice, salt, and water until the 

 tissue became frozen. Freehand sections were made with a razor. This method 

 of freezing tissues for microscopic work was superceded by methods which involve 

 the use of volatile fluids like ether. Instruments for the utilization of these fluids 

 were devised as attachments to the precision microtomes which were invented 

 after the use of celloidin and paraffin as embedding agents was discovered. 

 These instruments are still in use among histologists. In the hands of careful 

 workers they give satisfaction. They are, however, slow in action, expensive to 

 use, and easily put out of order. For these reasons, although almost all biolo- 

 gists have freezing attachments to their sliding microtomes, few make much use 

 of them. Of late, carbon-dioxide has been much utilized, especially by patholo- 

 gists, as a means of freezing tissues for sectioning. The convenience with which 



