APPENDIX TO THE HISTOLOGICAL SECTION. 113 



part, distilled water 10 parts, chromic acid (2i xc - solution) 10 parts, 

 and 1 drop of hydrochloric acid, ^ to 4 hours. This turns the blue 

 into an insoluble compound, and at the same time hardens the tissue. 

 A i" osmic acid solution may be substituted for the chromic acid ; 

 fixation then takes longer, as much as 24 hours. Tissues are then 

 washed, and may be stained in bulk in alum carmine, and are cut in 

 paraffin (avoiding long exposure to alcohol). 



27. Grain's method of staining bacteria and nuclear structures. 



1. Stain for 2 to 5 minutes in a solution of methyl violet in 

 2*5 P- C - carbolic acid solution in water. 



2. Transfer the preparation for 1 to 1'5 minutes into a solution of 

 iodine 1, iodide of potassium 2, water 300 parts. In this they turn 

 black. 



3. Differentiation in alcohol, until the colour has disappeared and 

 the preparation turns of a pale grey tint. 



4. Mount in Canada balsam. 



The feature of this process lies in the use of the iodine solution, 

 which transforms the previous diffuse stain into a selective one, by 

 acting as a mordant. 



Bacteria, nuclei (partially), especially those in mitosis, plasma cells 

 (Mastzellen), the horny layer of the epidermis and serous epithelium. 



A ground stain may be imparted to the cytoplasm of cells by adding 

 a little eosin to the last alcohol used in differentiating. 



This method can be used for blood films. 



28. Weig-ert's fibrin stain. Sections of tissue hardened in 

 alcohol treat as follows : 



1. Stain 5 to 10 minutes in saturated solution of gentian violet in 

 anilin water (anilin oil 5 cc shaken up with water 100 cc and filtered 

 until clear). 



2. Wash in 0'6P- C - NaCl solution. 



3. Dry on the slide with filter paper. 



4. Decolourise for 2 to 3 minutes in a solution of iodine in iodide 

 of potassium (1:2: 100). 



5. Dry with filter paper. 



6. Decolourise with anilin oil 1, xylol 2 parts. 



7. Remove the anilin-xylol with xylol. 



8. Mount in Canada balsam. 



29. Beneke's modification of the above, for general purposes. 

 The strength of the anilin decolourising solution is diminished by 

 mixing 2 parts of the latter with 3 of xylol. 



