148 IMBEDDING METHODS. 



an ingenious little instrument called a " section-stretcher." 

 This consists essentially of a little metallic roller suspended 

 over the object to be cut in such a way as to rest on its free 

 surface with a pressure that can be delicately regulated so as 

 to be sufficient to keep the section flat without in any way 

 hindering the knife from gliding beneath it. 



(See the description^ 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 GIESBEECHT) ; Arch.f. mik. Anat., xxiii, 1884, p. 537 

 (DECKER) ; Bull.Soc. Beige Mic., x, 1883, p. 55 (FRANCOTTE) ; The Micro- 

 scope, February, 1884, (GAGE and SMITH) ; WHITMAN'S Meth. in Mic. Anat., 

 1885, p. 91 ; Zeit. f. iviss. Mik., iv, 2, 1887, p. 218 (STRASSER) ; as well as 

 Journ. Roy. Mic. Soc., iii, pp. 450, 916, and other places). 



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 contained in the head or broad part, and the edge 

 turned towards the knife. 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. 



Alcohol helps sections to unroll, and so does carbolic acid ; 

 it is said that if they be brought into concentrated carbolic 

 acid after removal of the paraffin by benzin or turpentine, 

 they will unroll themselves safely and float flat on the surface 

 of the liquid. 



274. Chain or " Ribbon" Section-cutting. It is probably a 

 familiar fact to the majority of workers with the modern 

 microtomes that if a series of paraffin sections be cut in suc- 

 cession and not removed from the knife one by one as cut, 

 but allowed to lie undisturbed on the blade, it not unfre- 

 quently happens that they adhere to one another by the ecl^vs 

 so as to form a chain 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 chain. 

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

 certain relation to the temperature of the laboratory. 



Small sections can always be made to chain when cut from 



