VII. SUMMARY OF METHODS OF PREPARATION OF CELLOIDIN SECTIONS.
1. Fixation of the tissues in alcohol, formol, etc.
2. Wash 24 hours, when necessary.
3. After-harden in 80 and 95 per cent alcohols for 1 to several days.
4. Complete dehydration in absolute alcohol for 24 hours.
5. Equal parts of pure ether and absolute alcohol, 24 hours.
6. Thin celloidin, 1-3 days.
7. Thick celloidin, 1-3 days.
8. Block. Harden block in 80 per cent alcohol.
9. Cut; keep sections in 80 per cent alcohol.
10. Stain; differentiate.
11. Wash thoroughly.
12. Dehydrate in 80 and 95 per cent alcohols.
13. Final dehydration and clearing in carbol-xylol.
14. Place on slide and blot with absorbent paper.
15. Mount in xylol-balsam or xylol-colophonium.
VIII. SUMMARY OF METHODS OF PREPARATION OF PARAFFIN SECTIONS.
1. Fixation of the tissue in alcohol, formol, etc.
2. Wash 24 hours, when necessary.
3. After-harden in 80 and 95 per cent alcohol for 1 to several days.
4. Complete the dehydration in absolute alcohol for 24 hours.
5. Aniline-oil until tissue becomes transparent.
6. 1st. Xylol, ½ hour, to remove aniline oil.
7. 2nd. Xylol, 1-2 hours, until translucent.
8. 1st. Paraffin (52°C.), ½ hour in oven, to remove xylol.
9. 2nd. Paraffin (52°C.), 1-12 hours in oven, until infiltrated.
10. Imbed and block; cool quickly.
11. Cut sections; mount on slides or covers.
12. Remove paraffin in xylol.
13. Remove xylol in absolute alcohol.
14. 80 per cent alcohol, for a few minutes.
15. Stain; differentiate; wash.
16. Dehydrate in 80 and 95 per cent alcohols.
17. Clear in carbol-xylol.
18. Mount in Canada-balsam or colophonium.
IX. ARTEFACTS IN MOUNTED SECTIONS.
A mounted section, after passing through the various stages indicated above, must of necessity present some appearances that are the result of the technical methods employed. The number and degree of such artefacts will depend upon the character of the methods employed and the care exercised in their performance. The trained observer ignores the presence of artefacts as having nothing at all to do with the significance of the section itself; but to the beginner in microscopic work they often appear to be the most important thing in the preparation, and are given a pathologic interpretation. How frequently do we see students, undergraduates and postgraduates, take up a section and pick out a fold, wrinkle, tear, staining-defect, precipitate, dirt, etc., as pathologic features! It is necessary, therefore, for the student to acquaint himself with the nature of artefacts so that he may ignore them and not give them an incorrect interpretation. The most important artefacts are as follows:—
1. Artefacts due to fixation (mercuric, chromic, osmic, etc., precipitates; alterations in blood-pigment due to formol; loosening of cells from basement membrane due to contraction [kidney tubules, etc.: loosened endothelium in blood-vessels, particularly confusing to students]; destruction of red blood cells, as in alcohol fixation; poor staining due to over-fixation).
2. Artefacts due to hardening (contraction, desquamation of cells, etc.).
3. Artefacts due to imbedding and cutting (tears, holes, ragged edges, irregular thickness, knife-streaks, compression of soft structures, dislocation and tearing-out of firm tissues or material, wrinkles, folds, etc.).
4. Artefacts due to poor staining (uneven, spotted or streaked staining, overstaining, understaining, poor differentiation, precipitates, insufficient washing, fading, poor contrasts, defective staining due to presence of paraffin, dextrin, etc., in section).