300 



SUMMARY OF CURRENT RESEARCHES RELATING TO 



Em. 52. 



geometrical planes. It is still, however, of course desirable that as 

 much exactness as possible should be obtained iu these planes, as 

 their irregularities cannot fail to affect the sections, especially as they 

 are, in fact, multiplied in the latter. Prof. Thoma highly commends 

 Herr Jung, of Heidelberg, who makes the microtomes under his 

 instructions, for the great exactness which he has obtained.* 



As the efficiency of a newly-constructed instrument is best judged 



of by practical exi^erience of its capa- 

 bilities, Prof. Thoma (besides stating 

 generally that it has been found that 

 any one can produce sections of great 

 delicacy with this microtome without 

 previous practice), gives the following 

 facts : — Specimens which are well 

 hardened will allow of sections of 3 

 to 4 sq. cm. surface and 0-015 to 

 0*010 mm, thickness. In exceptional 

 cases, pieces of so large a surface may 

 even be cut of 0*005 mm. thickness. 

 If the section is smaller (for instance, 

 1 cm. square), the thickness can be 

 reduced considerably — say to 0*005 

 mm., or, in extreme cases, to half that. 

 It is not, however, all tissues and 

 objects that will admit of sections of 

 such delicacy. Well-hardened liver 

 may generally be cut to 0*015 mm., this being about the diameter of 

 the hardened cell. Occasionally, however, in this tissue, sections of 

 0*010 mm. can be obtained. Lymphatic glands and brain may be 

 cut to 0*010 or 0*075 mm.; embryonic tissues, well imbedded, 

 usually admit sections of * 005 and * 003 mm. In some cases even 

 sections of 0*002 mm. thickness can be obtained. These numbers 

 refer to the largest size of the microtome, and to serial sections. 

 The two smaller sizes will give sections of the same delicacy, but 

 comparatively smaller in extent of surface. The length of the sliding 

 surfaces of the large instrument is 40 cm., and the edge of the knife 

 is 23 cm. In the medium size these dimensions are 27 and 16 cm., 

 and in the smallest about 21 and 11 cm. 



Prof. Thoma also adds some practical remarks on the use of the 

 microtome, and the necessary previous preparation of the specimens, it 

 being his opinion that further progress in section-cutting is to be 



* Prof. Thoma remarks that at a time when already a number cf his micro- 

 tomes were in use, an instrument entirely dififerent in its general appearance, but 

 yet constructed on similar principles, appeared in America — the micrutonie of 

 Mr. Fletcher (Boston 'Medical and Surgical Journal,' 1880). The knife-carrier 

 elides on five points on the bottom of a large basin filled with alcohol. This 

 microtome shows such eminently diftereut qualities to the one explained here, that 

 the independence of the invention is on both sides very evident. The value of 

 the principle, however, is at the same time demonstrated by the relative good 

 results which have been obtained by this American machine. Its limit as regards 

 the thinness of the sections appears to be • 0004 in. 



Transverse Section of the Micro- 

 tome. — ss, stand ; a, carrier for the 

 knife; 6, carrier for the object; d, 

 screw to attach the knife ; e, axis 

 supporting the clump for the 

 object. 



