17 



68. Minot's Automatic Microtome. 



E. 53. 1889. Made by E. Zimmermann. 



The knife is stationary. The object carrier is attached to a 

 sliding base ; this and the driving wheel which actuates it are 

 both massive, and so .constructed that the object is caused to 

 move in a vertical plane, with the maximum downward pressure. 

 The forward displacement of the object carrier is effected at 

 every revolution of the driving wheel by means of a micrometer 

 screw. The wheel which turns the screw is actuated by a pawl 

 ftnd upright lever apparatus, under control of a set-screw which 

 bears a series of arms of graduating lengths. The working 

 parts may be so adjusted that a cutting capacity of from 

 0'04- mms. to 0*0033 mm. may be assured at will. The instru- 

 ment is provided with a ribbon receiver for paraffin sections, and 

 with six object carriers. 



69. Ryder's Automatic Microtome. 



E. 41. 1889. Made by J. Zentmayer. 



The object carrier is borne upon an oscillating lever, under 

 control of a spring, and so constructed that at every complete 

 oscillation the imbedded object is pulled down upon the razor, 

 previously fixed in position. The knife holder is so arranged 

 that the razor-edge may be set at any angle to the direction of 

 the paraffin block. The movements of the lever are adjusted by 

 a screw fixed to a toothed wheel of 3 in. diameter, and these are 

 actuated by a pawl fixed to the side of the lever. The number of 

 h which this pawl can pass in a single oscillation is determined 

 bv a stop attached to the und4r side of the lever, which, on being 

 caused to strike the bed-plate, brings the lever to rest at a 

 constant point for each movement in a downward direction. 



An adjustable sector is placed beside the toothed wheel, for 

 the purpose of throwing the pawl out of gear, and this is so 

 arranged that the necessary adjustments are effected at each 

 oscillation, before the imbedding material, with its contained 

 object, reaches the knife. 



Sections cut through the arc embraced by a single tooth of 

 the revolving wheel would have a thickness of 0-0025 mm. 



J. DRAWINGS OF MICROSCOPIC OBJECTS. 



70. Camera lucida drawings of microscopic objects. 

 Exhibited by R. and J. Beck. 1876. 



Leaf insect from sycamore. 

 Aearus from fly. 

 Flea from cat. 

 Tarsus of corn weevil. 



