ZOOLOGY AXD BOTANY, MICKOSCOPY, ETC. 699 



after the gum has frozen. The edge of the razor must be elevated to 

 the required height for cutting the section by means of the three 

 screu-s supporting the frame. After the first cut, each end of the 

 razor must be again presented to the surface of the specimen, when 

 either end of the blade can be adjusted by one of the centre screws 

 •nntil its entire length is level, tlaen by turning the larger screw at 

 the apex of the frame it can be lowered for each successive section 

 required. One entire revolution produces a section ytto o^ ^^ inch in 

 thickness. 



The screw-head being divided into sixths, one division gives a 

 section of -^^ of an inch, and thinner ones can be produced by pro- 

 portionately turning the screw. Substances that have been previously 

 prepared in spirit or chromic acid require to be steeped in syruj) for 

 twenty-four hours beforehand, otherwise they will not readily con- 

 geal. It is advisable to cover the apparatus with baize to facilitate 

 the operation of freezing. "When it becomes necessary to sharpen the 

 razor, it can easily be removed for that purpose, but when replacing 

 it, care must be taken to arrange it parallel and with the edge a trifle 

 lower than the back, so as not to deface the preparation. Too much 

 force must not be exerted in clamping the razor in position, as the 

 blade is liable to twist or bend. 



Zeiss's Microtome.* — Dr. Korting describes this instrument, the 

 first incentive to the construction of which originated with Professor 

 Lichtheim as a desirable improvement on the Leiser form. 



The microtome (Fig. 165) consists of a broad cast-ii'on foot a, to 

 which a brass upright h is screwed. To this is fixed, on the right, 

 a piece d, which is planed smooth, and allows the knife-carrier 

 (14 cm. long) to slide along it. To prevent it slipping oft', there is a 

 groove, in which moves a button attached to the under side of the 

 knife-carrier. The knife is fixed by the screw e, which clamps the 

 handle between two brass plates, the surfaces of which are plane and 

 smooth. "When the upper plate / is turned round e towards the left, 

 the knife can easily be taken out and put in. The knife itself is so 

 shaped that it can be held in the hand and used to make free-hand 

 sections if wanted. It most resembles the knife of Fritsch. The 

 blade can be fixed at angles between 62' and 24- to the sagittal axis 

 of the object. As the latter angle, especially when the object is very 

 delicate, does not exclude the pressing action of the knife to the 

 extent desired, Dr. Korting prefers for his instrument a knife whose 

 blade forms an obtuse angle of 1.50' with the handle. This can be 

 placed at such an acute angle with the object that 5 cm. out of the 

 7 cm. of the knife blade can be drawn tkrough an object 7 nun. in 

 diameter. 



To the left side of b a movable plate is attached, sliding between 

 two flanges, and to it the object-clamp is fastened. It is elevated by a 

 micrometer screw, a complete turn raising the object-carrier 0'3 mm. 

 The graduated head Ji, divided into 30 degrees, marks hundredths of 

 a millimetre in elevation. The clamp i can be turned about a pivot 



* Jen. Zeitschr. Xaturwi.^s., xiv. (ISSO) p. 193. 



