48 



ELEMENTS OF APPLIED MICROSCOPY. 



Once well imbedded, a cube of solid parafiin contain- 

 ing the object is cut out and fixed in a microtome, such 

 as is illustrated in Fig. 25. Several good instruments are 

 on the market, of which the Thoma and the Minot- 

 Blake types may be mentioned. In any case the knife 

 and object are firmly held in supports moving at right 

 angles to each other; and one or other of the supports is 



Fig. 25. — Thoma Microtome. (After Carpenter-Dallinger.) 



SO arranged that by some mechanical device it can be 

 shifted by. any desired amount between each excursion, 

 according to the thickness of the sections desired. If the 

 surrounding temperature be right, the successive sections 

 of paraffin will adhere by their edges, forming a long 

 ribbon. In such a ribbon each serial section represents 

 one plane in the original specimen; and the whole object 

 may thus be unrolled as it were upon the slide, each 

 structure being easily traced from section to section. 



Minute sections obviously cannot be handled by them- 

 selves. It is desirable, therefore, to affix them to the 



