PARAFFIN METHOD 87 



angle of which depends on the relation between the height of its 

 base and the distance from the base to the edge. With the same 

 base the angle becomes more acute the greater the distance from 

 edge to base. Now by slanting the knife we can effect what is 

 equivalent to an increase in the distance from edge to base ; for 

 we can thus increase the distance between the point of the edge 

 which first touches the object, and the point of the back (strictly, 

 of the back edge of the under cutting-facet) which last leaves it. 

 When the knife is set transversely, the line along which any point 

 of it traverses the object is the shortest possible from edge to base 

 of the wxdge, and the effective angle of wedge is the least acute 

 obtainable with that knife. But if it is set obliquely as possible, 

 the line along which any point of it traverses the object, traverses 

 the knife from heel to toe, that is, along the greatest possible 

 distance from edge to base, and therefore affords practically a 

 much more acute angled wedge than in the first case ; and so on, 

 of course, for intermediate positions. (See the sterometrical con- 

 structions of these relations by SCHIEFFERDECKER, Op. cit., p. 115 ; 

 and also with more instructive figures. Apathy, " Ueber die 

 Bedeutung des Messerhalters in der Mikrotomie," in Sitzber. 

 med.-naturw. Section d. Siebenbiirgischen Museumvereins, Bd. xix, 

 Heft 7, p. 1 (Kolozsevar, 1897, A. K. Ajtai). 



For honing knives see Ssobolew, Zeit. wiss. Mik., xxvi, 1909, p. 65 ; 

 Lendvai, ibid., p. 203 ; Funck, ibid., xxvii, 1910, p. 75. 



166. Very large objects are best cut with the slanting knife, and 

 so are all objects of very heterogeneous consistency, such as 

 tissues that contain much chitin or much muscular tissue ; and 

 better with a slowly working sliding microtome than with a quick- 

 working Rocker or the like. Soft masses such as gelatin or 

 celloidin cut wet, can only be cut with the slanting knife. The 

 slanting position causes less compression of sections than the 

 transverse one. It has the defect of producing rolling in paraffin 

 sections more easily than the transverse position. The latter 

 is the proper position for cutting ribbons of sections from 

 paraffin. 



167. By the tilt of the knife is meant the angle that a plane 

 passing through its back and edge makes with the plane of section : 

 or, practically, the greater or less degree of elevation of the edge 

 above the back (it is not to be confounded with the inclination 

 of the long axis of the knife to the horizon ; any accidental 

 inclination that this may have is a matter of no moment). 



The question of the proper tilt to be given to the knife under 

 different circumstances has been investigated by Apathy, loc. 

 cit. supra. He concludes — (1) The knife should always be tilted 

 somewhat more than enough to bring the back of the under- 

 cutting facet clear of the object. (2) It should in general be less 



