THE MICROSCOPIC PREPARATION. 



posure of the tissues to their action should be as brief as possible. The 

 paraffins most used have a melting point of 40 to 60 C. The kind of 

 paraffin used should depend upon the temperature of the room in which 

 the sectioning is to be done. It is even well to have different mixtures of 

 hard and soft paraffins at hand, so that, if the temperature of the room 

 be low, tissues may be imbedded in a softer mixture, and vice versa. 



The process of infiltrating and imbedding in paraffin is repre- 

 sented by the following diagram (instead of xylol, other intermediate 

 fluids may be used) : 



Alcohol, 90% 



t 



Abs. alcohol 



Alcohol-xylol mixture 



t 

 Xylol -< 



t 

 Xylol-paraffin (cold) 



t 

 Xylol-paraffin (in paraffin oven) 



t 

 Soft paraffin -^ - 



f 

 Hard paraffin 



t 

 Imbedding 



The size and density of the tissues must necessarily regulate the 

 length of time necessary for their proper infiltration. It is therefore hardly 

 possible to give any definite figures. In presenting the following table we 

 have taken as a standard any tissue that has the general consistency of 

 liver fixed in alcohol. The time is given in hours, and should in each 

 case be regarded as a minimum. A longer stay in any one fluid will, 

 under favorable circumstances, do no harm. 



2. CELLO1DIN. 



The best and most convenient celloidin to use in microscopic work is 

 Schering's granular celloidin, put up in i -ounce bottles. Of this a 

 stock or thick solution is prepared by dissolving 6 gm. of the celloidin in 

 100 c.c. of equal parts of absolute alcohol and ether. Of this, when 

 required, a thin solution is prepared by diluting a quantity of the stock 

 solution with an equal quantity of the ether and alcohol solution. 



