ANATOMICAL TECHNIQUE 455 



subsequent to removal from the edge of the knife, this disadvantage 

 may be largely obviated by allowing them nearly to dry on the 

 flat surface of the knife at some distance from the part of the edge 

 which is actually being used for cutting. 



In the case of hard and homogeneous material, such as wood, 

 pieces of nutshell, coal, etc., a special type of object-holder must 

 be used, in which the material is firmly held in a rigid clamp. Two 

 varieties of these have been devised for the Thoma microtome, 

 recommended for the purposes here described. One, contrived 

 by Professor R. B. Thomson, is made in Toronto, and particulars 

 in regard to it may be obtained by writing to the Botanical Depart- 

 ment of the University of Toronto. This is an admirable device 

 and is particularly useful in cutting large pieces of wood which 

 have not been sufficiently softened. A second type of holder for 

 hard objects has been devised by the writer and is manufactured 

 to order by the Jung Company of Heidelberg. In these holders 

 the position of the object can be varied so as to obtain the proper 

 inclination to the edge of the knife. For example, in cutting radial 

 sections of wood the slices obviously must be accurately parallel 

 to the rays, or else a very confused condition is presented under 

 the microscope. The object-carriers in both these holders are 

 very heavy in order to insure the necessary rigidity and inertia. 

 .A complete Thoma microtome with the additional holder for 

 cutting hard objects costs about one hundred dollars free of 

 American duty. With the Thomson devices the cost is consider- 

 ably greater. 



As has been pointed out in an earlier paragraph, wood and 

 similar tissues need not be infiltrated with nitrocellulose to secure 

 the best results. If, however, the woody tissues for any reason 

 have become unduly softened, either from too prolonged immer- 

 sion in hydrofluoric acid or through the ravages of fungi (this is, 

 of course, particularly the case where diseased or rotten wood is 

 being studied), imbedding in celloidin or collodion is necessary. 

 As will be shown in a later paragraph, this procedure is absolutely 

 necessary with most coals. The cutting of sections of very hard 

 tissues involves the same principles as exemplified in the technique 

 of smaller and less homogeneous objects, with the exception only 



