PARAFFIN METHOD 91 



Mark (Anier. Natural., 1885, p. 628 ; cf. Journ. Roy. Mir. Soc, 1885, 

 p. 738) gives the following directions : 



" Have ready a little very fluid collodion in a small bottle, through 

 the cork of which passes a small camel-hair brush, which just dips into 

 the collodion with its tip. The collodion should be of such a consistency 

 that when applied in a thin layer to a surface of paraflin it dries in two 

 or three seconds without leaving a shiny surface. It must be diluted 

 with ether as soon as it begins to show signs of doing so. 



" Take the brush out of the collodion, wipe it against the neck of 

 the bottle, so as to have it merely moist with collodion, and quickly 

 pass it over the free surface of the preparation. Care must be taken 

 not to let the collodion touch the vertical surfaces of the paralfin, 

 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 collodionised 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. 



Heider (Embryonalentw. v. Hydrophilus, 1889, p. 12 ; cf. Zeit. wiss. 

 Mik., viii, 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 (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 compli- 

 cated development of this process is described by Lendenfeld in Zeit. 

 wiss. Mik., xviii, 1901, p. 18. 



Apathy {Mikrotechnik, p. 183) employs a 1 per cent, solution of 

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

 process (§ 175). 



Jordan (Zeit. wiss. Mik.) adds 5 drops of oil of cedar to 15 c.c. of the 

 solution of celloidin, and finds that rolling is prevented. 



172. Collodionisation, as it has been called, is merely a palliative. 

 One may very aptly cite the old adage that " an ounce of pre- 

 vention is worth a pound of cure." With the methods now 

 available there is little excuse for attempting to cut hard or brittle 

 material for if the proper technique is employed in the first place 

 nearly all objects can be sectioned without the difficulties experi- 

 enced by earlier workers. 



Hardness and brittleness may be due to a number of causes. 

 First is the selection of an improper fixation method. The reader 

 will find in the various chapters of this book, adequate directions 

 for the best type of fixing fluid to be used for different animal and 

 plant tissues. If he lacks experience in these methods he should 

 read the proper section before attempting to fix a new type of 

 tissue. Second, ethyl alcohol has a tendency to harden tissues 



