2IO Journal of Comparative Neurology. 



contains the object holder. The knife has a width of 5 cm. and 

 a cutting edge of 30 cm. It requires from 1.5 to 2 litres of 

 fluid to fill the tank. In cutting, the knife is drawn back by a 

 treadle and when released "the weight and pulley gives the 

 cutting stroke," In the description referred to, the writer ^ays 

 " Exceedingly thin sections may be cut on it without skipping." 

 But he does not tell us just how thin. He further adds 

 that the object-holder is not sufficiently delicate in its adjust- 

 ment, for the finest embryological work. 



The machine we are about to describe was made two years 

 ago at Clark University, in response to the demand for a micro- 

 tome that would cut a whole human brain, in any plane, into 

 sections of, say, 50 micra thickness, without wasting a section 

 from beginning to end, and with the consequent possibility of 

 determining the location of every section. 



This instrument embodies two principles new to brain mi- 

 crotomes. First the brain is made to move instead of the knife. 

 Secondly, the knife is made to hold the fluid into which the 

 section is to be cut. The advantages of this arrangement are 

 easily seen. The blade being fixed at both ends can be made 

 sufficiently long and thick to insure a clean oblique ciit, without 

 sagging or springing out of correct position. Being placed 

 horizontal it can be flowed with alcohol, a small quantity being 

 sufficient to float the section. 



The details of construction and the modus operandi will be 

 readily understood from the following description and from 

 reference to the cuts. 



The finished microtome is 34 inches high and 35 inches 

 long, and is made wholly of iron. The cutting blade is made 

 of finely tempered steel, 36 inches long, 23^^ in. wide and 1/% 

 in. thick at the back. It is strongly concaved on the upper 

 surface, and slightly so on the under surface. To the back edge 

 is screwed a zinc pan flush with the concaved upper surface of 

 the blade. This with the concavity of the blade itself, forms 

 the receptacle for the alcohol into which the section slides as it 

 is cut. This pool is 8 inches wide, and 1^ inch deep at the 

 back, and in front shoals gradually to the very edge of the blade. 



