90 PARAFFIN METHOD 



170. See the descriptions of various forms of section-stretchers, 

 Zool. Anzeig., vol. vi, 1883, p. 100 (Schultze) ; Mitth. Zool. Stat. 

 Neapel, iv, 1883, p. 429 (Mayer, Andres, and Giesbrecht) ; Arch, 

 mik. Anat., xxiii, 1884, p. 537 (Decker) ; Bull. Soc. Belg. Mic, x, 

 1883, p. 55 (Francotte) ; The Microscope, February, 1884 (Gage and 

 Smith) ; Whitman's Meth. in Mic. Anat., 1885, p. 91 ; Zeit. wiss. 

 Mik., iv, 1887, p. 218 (Strasser) ; ibid., x, 1893, p. 157 (Born). The 

 best are those of Mayer and Born. 



Another plan is to allow the sections to roll, but to control the 

 rolling. To this end, the block of paraffin is pared to the shape of 

 a wedge five or six times as long as broad, the object being con- 

 tained in the broad part, and the edge turned towards the knife 

 (see Fig. 4). The sections are allowed to roll and come off as 

 coils, the section of the object lying in the outermost coil, which 

 will be found to be a very open one — indeed, very nearly flat. 

 Lay the coil on a slide with this end downwards, warm gently, 

 and the part containing the object will unroll completely and lie 

 quite flat. 



Anile (Glandole duodenali, Napoli, 1903, p. 51) and Vastaini- 

 Cresi {Mon. Zool. Ital., 1906, p. 164) lay a strip of wet filter- 

 paper on the block. 



Another defect is the compression and the crumpling or 

 puckering of sections, indicating that the paraffin has been 

 compressed by the knife instead of being merely cut true by 

 it. Such sections, besides showing creases or folds, have a 

 smaller area than that of the block from which they are cut. 

 This is a bad fault, for the compression may obliterate 

 important cavities or efface important limits between cell- 

 layers, etc. It may be caused by a badly cutting knife, and 

 is very easily caused by the paraffin being too soft. To prevent 

 it, correct the knife or cool the paraffin, or re-imbed in harder 

 paraffin. 



Very large sections tend to form folds on the knife, and are difficult to 

 remove from it. Mayer (Grundziige, Lee and Mayer, p. 94) gets 

 them to wrap themselves round a glass or gelatin tube laid on the block 

 just in front of the knife-edge and rolled forwards as it progresses. 

 Wlien cut, the section is rolled off on to the surface of water. 



171. Cutting Brittle Objects. Some objects are by nature so 

 brittle that they break or crumble before the knife, or furnish 

 sections so friable that it is impossible to mount them in the 

 ordinary way. Ova are frequently like this. One remedy 

 consists in covering the exposed surface of the object just before 

 cutting each section with a thin layer of collodion, which serves 

 to hold together the loose parts ; and will enable the operator 

 to cut sections considerably thinner than can be obtained in the 

 usual way. 



