CLOTH RED B 



84 



COAGULATION 



other. Of them xylol is by far the most 

 widely used and rightly so. Two 

 changes of half absolute alcohol and xylol 

 within 1 hr. and 2 changes of xylol within 

 the next 3-4 hrs. are usually sufficient 

 for slices of tissue 4-6 mm. thick, but the 

 time should not be extended beyond 

 that needed to attain translucency be- 

 cause so doing causes a hardening and a 

 shrinkage of the tissue. 



Several other substances can be used 

 in place of xylol. Cedar wood oil is ac- 

 cording to Lee (p. 80) the very best 

 clearing agent for paraffin imbedding. 

 It penetrates rapidly, does not make the 

 tissues brittle, and, when not entirely 

 displaced by paraffin, does not seriously 

 interfere with sectioning. First treat 

 the tissue with ^ absolute and xylol for 

 about 2 hrs. The time required in the 

 oil of cedarwood is however a little longer 

 than in the case of xylol used alone, say 

 12 hrs. Some recommend 2 changes of 

 xylol (about 30 min.) after the oil of 

 cedarwood before entering ^paraffin and 

 cedarwood oil. 



Methyl benzoate is now quite popular. 

 Pass the tissue from absolute alcohol 

 through 2 changes of pure methyl ben- 

 zoate within 12-24 hrs. When it has 

 been definitely cleared remove benzoate 

 by 2 changes of benzol (^-1 hr.) before 

 passing into paraffin, or half benzol and 

 paraffin. 



Chloroform penetrates pxaorly and 

 should not be employed unless called for. 

 It has the further disadvantage that 

 unless completely removed in the paraf- 

 fin bath, it will make the final paraffin 

 block soft and unfit for cutting. The 

 usual practice is to clear very small 

 pieces for about 12 hrs. in 2 changes, or 

 as long as may be necessary to make 

 them transparent, and in the imbedding 

 to use 4 changes of paraffin. 



A more rapid method is to pass di- 

 rectly from the fixative, Bouin or forma- 

 lin, without washing, to 3 changes of 

 pure dioxan within 4 hrs. and thence 

 into 3 changes of paraffin as advised by 

 Graupner, H. and Weissberger, A., 

 Zool. Anz., 1931, 96, 204-206. Stowell, 

 R. E., Stain Techn., 1941, 16, 67-83 

 confirms and extends earlier work of 

 Seki which shows that, although xylol 

 shrinks tissues more than dio.xan, in 

 placing in hot paraffin, the final shrink- 

 age is greater in tissues after dioxan. 

 When great haste is necessary Mallory 

 (p. 54) suggests acetone \-2 hrs. ; benzol, 

 15-30 min. ; and paraffin 3 changes, 30-90 

 min. The shrinkage, however, is very 

 marked and it would probably be better 

 to use Frozen Sections. 



By the Altmann-Gersh technique, 

 which is at once very time consuming 



and very valuable for special purposes, 

 fixation, alcoholic dehydration and clear- 

 ing can be side stepped and the dried 

 tissue directly impregnated with 

 paraffin. 



2. As the step following dehydration 

 of sections before mounting. The clear- 

 ing is of course easier and much quicker 

 owing to the thinness of the tissue. 

 Again xylol comes first and will probably 

 not be displaced though some prefer 

 toluol. It is not necessary to protect 

 against shrinkage and brittleness. 

 When desired, abs. ale. can be omitted 

 and the clearing be done from 90 or 

 even 80% ale. with terpineol, clove oil, 

 anilin oil, beech wood creosote, Bergamot 

 or some other substance. 



3. As a means of rendering clearly 

 visible certain structures in embryos or 

 whole tissues. Clearing is generally 

 done by the Spalteholz method. See 

 Cartilaginous Skeleton and Ossification 

 centers. When glycerin mixtures are 

 employed as Mounting Media they also 

 clear the tissues. See Groat, R. A., 

 Stain Techn., 1941, 16, 111-117 for clear- 

 ing tissues with mixtures of tributyl 

 and tri-o-cresyl phosphates. 



Cloth Red B (CI 262). A sulfonated azo 

 dye. For formula and influence on 

 mouse tumors, see Stern, K., Cancer 

 Res., 1950, 10,565-570. 



Cloudy Swelling. This is a marked swelling 

 and granulation of the cytoplasm of 

 cells. It is sometimes observed post- 

 mortem in acute febrile conditions 

 especially in the kidneys, liver and m5'o- 

 cardium. An almost meaningless syno- 

 nym, often used, is Parenchymatous 

 Degeneration. The extent of cloudy 

 swelling that may occur in vivo and 

 from which the cells may recover is 

 not known. The fatty droplets present 

 can be demonstrated in Sudan stained 

 frozen sections of formalin fixed mate- 

 rial. Special stains for Fibrin, Myo- 

 fibrils and Mitochondria may be de- 

 sirable. 



Coacervates (L. acervus, a cloud or swarm) 

 are masses of particles clumped together 

 (but encased in a little water) by a 

 change in their electrical charge while 

 in colloidal suspension in water or 

 by dehydration with resultant loss 

 of loosely bound water. Ilirsch (G. 

 C, Form und Stoffwechsel der Gol- 

 gi-Korper. Protoplasma Monographs, 

 Berlin, 1939) has likened the Golgi 

 apparatus to a coacervate. See Bensley, 

 R. R., Anat. Rec, 1937, 69, 341-353 for 

 critical consideration of suggestion that 

 mitochondria are coacervates. 



Coagulation. A phenomenon frequently 

 encountered in the case of blood and 

 lymph is of wide occurrence and is in- 



