36 FIXATION 



experiments carried out with gels cast in pessary moulds are 

 shown in fig. i. The fixatives acted for 18 hours. Those fixatives 

 that are not aqueous solutions are seen to shrink the gels, while 

 the acids, especially acetic acid, swell them strongly; the two 

 saturated aqueous solutions (picric acid and mercuric chloride) 



FIG. I. Graphical representation of the changes in 



volume undergone by gelatine/albumin gels during 18 



hours in various fixatives used at the concentrations 



shown on p. 24.^* 



change the volume least. The swelling eff'ect of acids is progressive. 

 A simple aqueous gelatine gel (15% w/W) shows the effect well. A 

 gel cast in a pessary mould swelled in acetic acid solution to about 

 13 times its original volume in a week. 



Gelatine/albumin gels placed in distilled w^ater increase in 

 volume by about 40% in 18 hours. If sodium chloride is added to 



