858 



SCIENCE. 



[N. S. Vol. V. No. 127. 



I. THE AUTOMATIC WHEEL MICROTOME 



This instrument was designed in 1886 

 and was first made by G. Baltzer, the 

 trusted instrument-maker of Professor Carl 

 Ludwig. Baltzer, wlio died recently, con- 

 tinued for many years to furnish, apparatus 

 for the Physiological Laboratory in Leipzig, 

 and had, therefore, unusual experience in 

 the practical construction of new instru- 

 ments. The first automatic microtome 

 made by him is still in active service in my 

 laboratory. Experience suggested various 

 minor improvements, which have contrib- 

 uted to render the microtome more accu- 

 rate and more convenient. Besides the 

 changes which I have introduced, there 

 have been several proposed by Professor 

 Wilhelm His and by Dr. Spalteholz, which 

 have proved especially valuable. It is re- 

 markable that very few available sugges- 

 tions have been made by the mechanics 

 who have manufactured the machines 

 hitherto. The most important change, I 

 consider, to have been the increase in the 

 heaviness of the construction, for it secures 

 greater rigidity, a quality of great impor- 

 tance when very thin sections are desired. 



Mr. Francis Blake, of Weston, Massachu- 

 setts, is engaged in improving the mechani- 

 cal construction of the instrument. The 

 changes proposed by him will prOve, I 

 think, of great value. 



The automatic microtome is now made 

 in Boston, by the Franklin Educational 

 Company ; Leipzig, by E Zimmerman ; 

 Paris, by E. Cogit ; Cambridge, England, 

 by the Cambridge Instrument Company. 



Over two thousand are now in use. I 

 believe that the instruments are in all cases 

 well made. I have not, however, had an 

 opportunity of testing myself those made in 

 England. The first instruments made in 

 America were not wholly satisfactory, but 

 I believe them now to be made in this 

 country fully as well as elsewhere, and 

 there are certain details in the American 



design, as at present followed, which render 

 it, in my judgment, preferable to the Euro- 

 pean models. The illustrations give two 

 views of the American microtome, as now 

 made. The general principle of the instru- 

 ment is to keep the knife fixed, and to move 

 the object to be cut in a vertical direction, 

 supplying it to the knife by an automatic 

 feed. The knife is carried by two upright 

 standards, united by two cross bars ; in the 

 American microtome these are all a single 

 casting ; in the German they are four sep- 

 arate pieces screwed together, and, there- 

 fore, less securely rigid. The two uprights 

 can be adjusted as to their distance from 

 the object to be cut. The object, imbedded 

 in paraffine, is attached to a brass plate, 

 which can be securely clamped at any de- 

 sired angle in the machine. The motion of 

 the apparatus is imparted by a wheel, which 

 may be turned by hand, or by a water or 

 electromotor, but the hand-power is the 

 most satisfactory. The wheel is made con- 

 siderably heavier and is better balanced in 

 the American model than in the others, so 

 that the machine works more smoothly and 

 evenly to the sensible improvement of the 

 cutting. The wheel turns the axle to which 

 it is attached, and at the opposite end of 

 the axle is a crank working a slide, which 

 raises and lowers the vertical carriage. 

 This carriage is held by adjustable gibs 

 against the vertical ways ; it carries on the 

 side toward the knife the object-holder, with 

 its adjustments to fix the plane of the sec- 

 tions ; it also carries the horizontal micro- 

 tome screw. The head of the micrometer 

 screw is a tooth-wheel, each tooth cor- 

 responding to a feed of ^-^ mm. The 

 screw is turned by a pawl, which acts upon 

 the toothed- wheel ; the pawl is worked, as 

 may be readily seen in Fig. 2, by the ver- 

 ticalmotion of the carriage, and the number 

 of teeth caught at each rise of the carriage 

 may be varied mechanically from one to 

 six. The American form of pawl is simpler, 



