96 CHAPTEFf VIII. 



surfaces of the paraffin, especially not the one which is turned 

 towards the operator, as that will probably cause the section 

 to become stuck to the edge or under- surface of the knife. 

 As soon as the collodion is dry, which ought to be in two or 

 three seconds, cut the section, withdraw the knife, and pass 

 the collodion brush over the newly exposed surface of the 

 paraffin. Whilst this last layer of collodion is drying, take 

 up the section from the knife and place it with the collodion- 

 ised surface downwards on a slide prepared with fixative of 

 Schaellibaum. Then cut the second section, and repeat the 

 manipulations just described in the same order." 



Henking {Zeit. wiss. Mik., iii, 1886, p. 478) takes instead of collodion 

 a solution of paraffin in absolute alcohol. 



For extremely brittle objects, such as ova of Phalangida, he recom- 

 mends a thin (light yellow) solution of shellac in absolute alcohol. 



Heidee (Embryonalentw. v. Hydrophilus, 1889, p. 12; cf. Zeit. iviss. 

 Mile., viii, 1892, p. 509) employs a solution made by mixing a solution of 

 gum mastic in ether, of a syi'upy 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 (of about 

 100° C). This has the advantage of filling up any cavities there may be 

 in the objects, and also of preventing the sections from rolling. A com- 

 plicated development of this process is described by Lendenfeld in 

 Zeit. wiss. Mile., xviii, 1901, p. 18. 



Apathy (Mihrotechnih, p. 18.3) employs a 1 per cent, solution of 

 celloidin, allows the sections to roll, and unrolls them by the water- 

 process (§ 149). 



Jordan (Zeit. wiss. Mik.) adds 5 drops of oil of cedar to 1-5 c.c. of the 

 solution of celloidin, and finds that rolling is prevented. 



148. 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 unfrequeutly 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. 

 For the production of a ribbon, the paraffin must be of a 

 melting-point having the right relation to the temperature of 

 the laboratory, see § 151. Secondly, the hiife shoidd he set 

 nquare. Thirdly, the block of paraffin should be trimmed so 

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



