3l8 APPENDIX 2 



To the 4% nucleoprotein solution add two-thirds of its volume 

 of distilled water. 



Make up the following fixatives at twice the concentrations given 

 on p. 24: — hydrochloric acid, nitric acid, trichloracetic acid, 

 chloroplatinic acid, chromium trioxide, formaldehyde, osmium 

 tetroxide, potassium dichromate, acetic acid. 



Put 5 ml of the diluted nucleoprotein solution in a test-tube and 

 add an equal volume of the fixative solution to be tested. (The 

 experiment may be done with smaller quantities when osmium 

 tetroxide or chloroplatinic acid is being tested, on account of the 

 high cost.) Close the tube and turn it upside down once. The 

 fixative will now be at the concentration shown on p. 24. 



Note the appearance of the contents of the tube immediately, 

 and again the next day. 



A different technique is necessary with fixatives that are used in 

 practice at or near saturation or unmixed with water; namely, 

 picric acid, mercuric chloride, methanol, ethanol, and acetone. To 

 test these, put 3 ml of the 4% nucleoprotein solution (undiluted) 

 in a test-tube and add 7 ml of the fixative at the concentration 

 shown on p. 24. It will be noticed that the amount of dry nucleo- 

 protein in the tube is the same as in the experiment described in the 

 preceding paragraphs (o-i2 g.) Close the tube and turn it upside 

 down once. Record the result as before. 



The results of these experiments are recorded in table 2 (p. 35). 



The penetration of fixatives into gelatine j albumin gel 



Cut glass tubing, about 0-7 mm in internal diameter, into short 

 lengths (about 45 mm long is suitable). Make a transverse mark 

 with a diamond near one end of each tube, and scratch on a dis- 

 tinguishing number. Put a rubber pipette-bulb on the marked end. 

 (Each tube will be called a pipette, though it is not narrow at the 

 tip.) See fig. 2, p. 38. 



Melt the gelatine-albumin gel (p. 314) at 37"^ C and draw it into 

 the pipettes. Support them vertically until the fluid has solidified. 

 (The exact position of the top of the gel is of no consequence, but 

 the tube must be filled nearly or quite to the bottom. There 

 should be no gel within the rubber bulb.) 



Measure and record the distance from the transverse diamond- 

 mark to the bottom of the gel. Measurements should be made to 

 the nearest quarter of a millimetre. 



Pi'.t 150 ml of the fiixative to be tested in a large specimen- tube. 



