APPENDIX 2 



EXPERIMENTS ON FIXATION 



CONTENTS 



Preparation of gelatine/albumin gel P^^S^ 314 



Preparation of nucleoprotein 314 



Preparation of gelatine/nucleoprotein gel 315 



The coagulation of egg-albumin by various fixatives 315 



The coagulation of egg-albumin by ferric sulphate 316 



The coagulation of egg-albumin by mercuric chloride 317 



The coagulation of nucleoprotein by various fixatives 317 



The penetration of fixatives into gelatine/albumin gel 318 

 The action of formaldehyde in rendering albumin not 



coagulable by ethanol 320 



Preparation of gelatine j albumin gel 



Dilute white-of-egg with twice its volume of distilled water. 

 Centrifuge the solution until the supernatant is clear. To 100 ml 

 of the supernatant add 15 g of powdered gelatine. Leave for i 

 hour; then place in an incubator at 37° C and stir from time to time 

 until the gelatine has dissolved. Filter through a cloth. 



Pour the gel into metal pessary-moulds. The 30-grain size is 

 convenient for most purposes. Cool in a refrigerator and remove 

 the separate gels. Each has a volume of about 1-87 ml. Keep the 

 gels in the refrigerator until required. They may be kept for 

 several days, but moulds eventually grow^ on them. 



The refractive index of this gel is about i'365. The protein 

 content is about 19-4%. 



Preparation of nucleoprotein 



Separate the fat from the fresh thymus glands of four or five 

 calves. Pass the glands through a domestic mincing-machine. 

 The instructions given below refer to 100 g of minced tissue. 



Grind up the mince for a quarter of an hour in a mortar w^ith a 

 roughly equal volume of washed sand. Put the ground material in 

 a flask and add 1000 ml of distilled water and i ml of chloroform 

 (the latter to check decay). Shake vigorously from time to time 

 over a period of about 20 hours. 



314 



