59. Difficulties in sectioning, (a) Rolling of the sections indicates too 

 hard a paraffin, tissue or both, or too low a cutting temperature; bring the 

 source of heat nearer or await better conditions, (b) Crushing together of the 

 sections or wrinkling. Too soft a paraffin, too high a temperature, imperfect 

 infiltration: alter conditions or reimbed, or reinfiltrate, etc. (c) The sections do 

 not ribbon. Due usually either to (a) or to a failure to have the two sides of the 

 block trimmed parallel and set parallel to knife edge, (d) The sections crack 

 parallel to knife edge: tissue very brittle, (e) The sections are electric. The 

 electricity is mainly due to friction in the cutting. The hardness of the tissue, 

 in some cases due to presence of metallic salts, or imperfection in the knife edge 

 seem in many cases to be responsible; although in many instances the cause 

 appears obscure. A tube of radium or a strong induction coil operating in the 

 immediate neighborhood is said to obviate the difficulty. 



Remember to have the paraffin block trimmed with two sides 

 parallel and the knife edge parallel to these. Also, do not attempt 

 to cut if the temperature of the room is too high, above 23 C. 



60. Resume of the method. To obtain as good results as 

 possible with a certain organ fixed and hardened in a certain way, 

 the steps must be carefully and exactly followed. Let the dehydra- 

 tion be complete, clearing thorough, infiltration sufficient; imbed, 

 carefully observing the three cautions mentioned; and in cutting, 

 remember to have a sharp knife, a cool room, and the imbedding 

 block properly trimmed. Success also depends largely on the pre- 

 vious treatment in the fixer and on the care with which the fixer is 

 washed out. 



Properly employed, the paraffin method is widely serviceable, 

 being only useless where the tissue is very large, very hard, hard- 

 ened or injured by heat, or w^here the exact form of a large organ is 

 important. 



THE CELLOIDIN METHOD. 



61. A comparison with the paraffin method has already been 

 given ( 47, 48); there may be emphasized here three points: (1) 

 w r ith paraffin heat is required, with celloidin no heat; (2) paraffin 

 must be removed from the sections subsequently, celloidin need not be 

 and usually is not dissolved out; (3) by the paraffin method may 

 be obtained small sections (5 cm. square or less), and thin, by the 

 celloidin, larger sections, but thicker. With paraffin heat (melting 

 and cooling) is necessary, and the mass is sometimes spoken of as a 

 fusion imbedding mass; celloidin is a solution, and the mass is left 

 in the tissues by evaporation, or its equivalent. 



