CH. XI] MICROTOMES AND SECTION KNIVES 371 



knives held in the hand. They dealt also with fresh tissue more 

 largely than we do at the present day, and learned also to distinguish 

 tissues by their structure rather than by their artificial coloration. 



It was not, however, on account of the lack of elaborate mechanical 

 devices for sectioning and complicated staining methods of the present 

 day, but because they put intelligence and zeal into their work that 

 made them so successful. 



If the reader is interested in the mechanical means for sectioning 

 he is referred to Dr. C. S. Minot's papers on the history of the micro- 

 tome in the Journal of Applied Microscopy, Vol. VI, and to Gilbert 

 Morgan Smith's article in the Transactions of the American Micro- 

 scopical Society, Vol. XXXIV, 1915, on the Development of Botanical 

 Microtechnique, pp. 71-129, 16 pages of bibliography; 18 figures, 

 showing early microscopes and microtomes. 



604. Types of microtomes. There are two great types: (i) 

 The early type in which the preparation to be sectioned is held me- 

 chanically and moved up by a screw, the section knife being held in 

 the hand and moved across the object, usually with a drawing motion 

 as in whittling. 



(2) The mechanical type, in which both specimen and knife are 

 mechanically held and guided, and the operator simply supplies 

 power to the machine, or when an electric motor is used the operator 

 starts and stops the machine and uses his hands in taking off the 

 ribbon as it is cut. The ribbon is wound on a cylinder or cut inta 

 the proper lengths for the slide trays (fig. 206-207). 



In the highest types of the second class automatic microtomes 

 the operator only needs to put the knife and specimen in position 

 and sections of any thickness and any number may be produced in 

 a short time. A skilled and experienced person can get better results 

 here as well as with free-hand sectioning or the hand microtome. 

 Even automatic machines work better for skilled workmen. 



In some forms the knife of these automatic microtomes is fixed 

 in position and the object to be sectioned moves, while in other 

 forms the object to be sectioned remains fixed and the knife moves. 

 Furthermore, for sectioning paraffin, the' knife meets the object 

 like a plane (straight cut), while for collodion sectioning the knife 



