112 CHAPTER VIII. 



For extremely brittle objects, such as ova of Phalangida, 

 the same author recommends a thin (light yellow) solution of 

 shellac in absolute alcohol. 



HEIDER (Embryonalentw. v. Hydrophilus, 1889, p. 12; cf. 

 Zeit. f. iviss. Mik , viii, 4, 1892, p. 509) employs a solution 

 made by mixing a solution of gum mastic in ether, of a 

 syrupy consistency, with an equal volume of collodion, and 

 diluting the mixture with ether until quite thin and liquid. 



RABL (ibid., xi, 2, 1894, p. 170) employs superheated 

 paraffin, kept at a temperature of about 100 C. on a water- 

 bath. This plan has the advantage of efficiently filling up 

 any cavities there may be in the objects, and also of prevent- 

 ing the sections from rolling. 



APATHY (Mikrotechnik, p. 183) employs a 1 per cent, 

 solution of celloidin, allows the sections to roll, and unrolls 

 them by the water-process. 



137. Ribbon Section-cutting. If a series of paraffin sections 

 be cut in succession and not removed from the knife one by 

 one as cut, but allowed to lie undisturbed on the blade, it 

 not unfrequently happens that they adhere to one another 

 by the edges so as to form a chain or ribbon which may be 

 taken up and transferred to a slide without breaking up, 

 thus greatly lightening the labour of mounting a series. The 

 following appear to me to be the factors necessary for the 

 production of a ribbon. 



Firstly, the paraffin must be of a melting-point having a 

 certain relation to the temperature of the laboratory. I find 

 that small sections can always be made to chain when cut 

 from a good paraffin of 45 C. melting-point in a room in 

 which the thermometer stands at 16 to 17 C., and that, for 

 the Thoma microtome, at 15 C. the paraffin is a trifle hard. 

 But see on this point 141. Secondly, the knife should be 

 set square. Thirdly, the block of paraffin should be pared 

 down very close to the object and should be cut so as to 

 present a straight edge parallel to the knife edge ; and the 

 opposite edge should also be parallel to this. Fourthly, the 

 sections ought to be jyut rapidly, with the swiftest strokes ^ 

 that can be produced. For it is the sharp impact 1 of the 

 knife that slightly heats, and therefore slightly softens the 

 near edge of the paraffin, and thus causes the sections to 



