THE PARAFFIN METHOD 117 



purpose. Cedar oil and chloroform may, in some cases, be as good as 

 xylol. 



Only a small quantity of the clearing agent is necessary, enough to 

 cover the material being sufficient; but since the grades, except pure 

 xylol, can be used repeatedly, it is better to use four or five times the 

 bulk of the material. Filter as in case of the alcohols. 



The transfer from absolute alcohol to the clearing agent should be 

 gradual, like the hardening and dehydrating processes. The most sue- * 

 cessful workers have been making this transfer more and more gradual. 

 Thirty years ago it was customary to transfer from absolute alcohol 

 directly to xylol; then a mixture of equal parts of absolute alcohol and 

 xylol was interpolated ; in the second edition of this book three grades 

 were placed between the absolute alcohol and xylol. It is undoubtedly 

 better to make the transfer still more gradual. The following series 

 seems to be safe, 2|, 5, 10, 15, 25, 50, 75, and 100 per cent xylol. These 

 mixtures of absolute alcohol and xylol can be made with sufficient 

 accuracy without measuring in a graduate. The 50 per cent grade is 

 made by mixing equal parts of absolute alcohol and xylol; the 25 per 

 cent, by adding to the 50 per cent an equal volume of absolute alcohol ; 

 make the 10 per cent grade from the 25 per cent by adding a little 

 more than an equal volume of absolute alcohol ; in the same way, make 

 the 5 per cent from the 10 per cent, and the 2| per cent from the 5 per 

 cent. The different grades may be kept in bottles and may be used 

 repeatedly. A couple of drops of safranin dissolved in absolute alcohol, 

 added to the 50 or 75 per cent xylol, will color the material a little and 

 will often be helpful in orienting after the imbedding in paraffin. 



Three grades a day, morning, noon, and night, will do for all the 

 grades, except pure xylol. It will do no harm to leave the material 

 overnight in any of the grades. The pure xylol should be allowed to act 

 for 10-24 hours, with 3 or 4 changes. This xylol can be used to make 

 up any of the lower grades. 



Throughout the dehydrating and clearing it is a good plan to keep 

 the material in Number 4 shells, which are made from glass tubing 

 about 25 mm. in diameter. Other clearing agents may be used, but the 

 process must be just as gradual. 



THE TRANSFER FROM CLEARING AGENT TO PARAFFIN 



This should also be a gradual process. The most convenient method 

 is to place a small block of paraffin in the pure clearing agent with the 



