REACTIONS OF FIXATIVES WITH PROTEINS. 



39 



gel. If nucleoprotein be substituted for albumin, however, the 

 limit of fixation is clearly seen. For the method of preparing 

 gelatine/nucleoprotein gel, see Appendix, p. 315. 



Since potassium dichromate is not a fixative of gelatine, albumin, 

 or nucleoprotein, this method cannot be used to measure its rate 

 of penetration. 



It is convenient to make observations at 2-, 3^, 4^, and 5^ hours, 

 and so on, if desired, up to 12- hours. If the distance penetrated is 



HOURS 



FIG. 3. Graph showing the rate of penetration of fixatives into gelatine/ 



albumin gel (acetic acid into gelatine/nucleoprotein gel). The fixatives 



were used at the concentrations shown on p. 24.^^ 



plotted as ordinate against an abscissa divided into equal parts 

 representing o to i, i to 2^, 2^ to 3^, 3^ to 4^, and 4^ to 5^ hours, 

 etc., the results can be shown as lines that would be straight if the 

 equation d = K^/t were exactly obeyed. It will be seen from 

 fig. 3 that the lines are nearly straight. It is probable that they 

 would have been even more nearly so if the temperature of the 

 room had remained constant. The only substance that does not 

 show general obedience to the equation is osmium tetroxide. The 

 fixed gel in this case appears to offer some resistance to penetration, 

 for the curve falls with the passage of time. Up to 4^ hours, the 

 ^- value is fairly constant at i-o, but from 4^ to 12^ hours only 

 0-31. 



The values of K are shown below. The figures are based on 



