June 1, 1897.] 



SCIENCE. 



861 



sections will then jump at any neighbor- 

 ing object, especially of metal, and adhere 

 to it obstinately. Sometimes the force is 

 sufficient to break a ribbon of sections, 

 which will then snap at the microtome and 

 in an instant be clinging to it in a hopeless 

 snarl. The amount of electrification varies 

 from day to day, and there are fortunately 

 days during which the phenomenon is ab- 

 sent. Usually damp days are the best. 

 The cutting of any valuable object should 

 be reserved for one of the favorable days. 

 By laying an inclined plane, some ten inches 

 long, of wood or cardboard, with its upper 

 edge under the knife and its lower edge 

 resting on the table, it will be found that 

 the ribbon of sections, even if electrified, 

 can be handled with comparative safetj^ for, 

 even if the sections are drawn down by the 

 electrical attraction, they will lodge upon 

 the plane and usually will become either 

 twisted or entangled. 



II. THE PRECISION MICROTOME.* 



The first object of a microtome is to make 

 sections of even and known thickness ; the 

 second object is to make a sections in large 

 numbers of uniform thickness ; the third 

 object is to make sections rapidly. Finally, 

 in recent years, there has been a growing 

 and justified demand for microtomes to 

 make good sections of extreme thinness, if 

 possible not over one five-hundredth of a 

 millimeter or two microns (0.002 mm.). 

 Sections of such tenuitj^ and even possibly 

 of less thickness have been made hitherto 

 with the microtomes now in use, and I have 

 not infrequently encountered the statement 

 that the requisite precision was already 

 secured by one or another pattern of micro- 

 tome. In looking at such sections I have 

 observed in a number of cases that they 



*This instrument has been shown at Paris, Liver- 

 pool and before the Society of Morphologists at Bos- 

 ton. See Comptes Eendus Soc. Biologie, Paris, 1896, 

 Juin, p. Report British Assoc. Adv. Sci., Liverpool, 

 1897, p. 979. Science, N. S., Vol V., p. 106. 



were much thicker than they were stated 

 to be, and have learned upon inquiry that 

 the scale of the microtome was unknown to 

 the operator. In other cases the sections 

 appeared to be really as thin as stated, but 

 such as I have seen were invariably of 

 minute objects, which offered no real diffi- 

 culty to fine sectioning. I do not think 

 any form of microtome hitherto constructed 

 can be relied upon to yield sections 0.002 

 mm. thick of objects that are of even mod- 

 erate size or that offer much resistance. 



The first step was to gain a more definite 

 notion of the practical hints of admissible 

 error. Now, upon trial it was found that 

 sections which vary more than one- tenth 

 from their supposed thickness can, in the 

 case of stained animal (vertebrate) tissues, 

 be readily recognized by the naked eye as 

 uneven. Hence, it is obvious that the thin- 

 ner the section the less must be the amount 

 of absolute error in the cutting. For ex- 

 ample, an error of 0.0002 mm. is the maxi- 

 mum admissible for sections of 0.002 mm. 

 (500 to a millimeter), though a much 

 greater error would not be noticeable in 

 sections of 0.02 mm. Applied to the micro- 

 tome this means that a roughly made in- 

 strument is sufficient for thick sections, but 

 the most perfect construction is necessary 

 to secure a microtome for fine cutting. Be- 

 sides, for greater mechanical perfection, a 

 new microtome should also strive to be so 

 constructed as to be suitable for both dry 

 (paraffiie) and wet (celloidine) cutting. 



It seemed to me that progress might be 

 made on the basis of the following principles: 



First: The object should be supported 

 directly under the knife, and upon a car- 

 riage with. a broad base. 



Second : The carriage should move upon 

 a horizontal way below the knife. 



Third: The object should be fed to the 

 knife by a vertical micrometer screw, which 

 should be arranged to work automatically. 



Fourth: The knife should be firmly 



