38 FIXATION 



penetrated, d, is a-b in fig. 2. It is to be noted that the distance 

 measured is not necessarily the same as the depth of the fixed 

 protein: that would only be so if the process of fixation caused no 

 swelling or shrinkage. 



A 



B 



DIAMOND 

 MARK 



FIXED GEL 



UNFIXED GEL 



FIG. 2. Pipettes used in the measurement of the 



rate of penetration of fixatives into gelatine/ 



albumin gel.^^ 



A, the pipette filled with gel, before being placed in the 

 fixative. B, the pipette after immersion for a period in a 

 fixative. If the fixative is a protein-coagulant, the line of 

 demarcation between unfixed and fixed gel can be seen, 

 c, the glass tube has been turned upside down and the 

 unfixed gel has run out. 



The distance the fixative has penetrated is a-b. 



The measurement of the rate of penetration of noncoagulant 

 fixatives is more complicated. When the fixative has acted for a 

 particular time {i), the tube is lifted out; the pipette-bulb is 

 removed and placed on the other end of the tube. The tube is then 

 floated in water maintained at 37° C. The unfixed gel soon melts 

 and runs out; the fixed part remains in the tube (fig. 2, c). 



Acetic acid fixes neither gelatine nor albumin, and its rate of 

 penetration can therefore not be measured with gelatine/albumin 



