PARAFFIN EMBEDDING 271 



or so \atvv this is (•lianii;e(l to 100 per criit alcohol. This has no 

 water in it, and when (hfi'used throujijh the tissue, water will have 

 been removed. This process of dehydration must not be too rapid 

 or distortion, caused by too rapid withdrawal of water, may occur. 

 The alcohol may also exert an effect on sonic of the protoplasmic 

 substances which have been preserved but not precipitated or 

 coagulated by the fixati\es. Tissues should not remain too long 

 in the higher alcohols, /'. e., 95 and 100 ])er cent. 



Paraffin does not mix with alcohol; therefore, some other common 

 chemical must be employed that is miscible with alcohol and paraffin 

 which can be used to transfer the object from alcohol to paraffin. 

 Xylol or benzene can be used for this purpose. Xylol is preferable, 

 since it is not so inflammable as benzene, although benzene causes 

 less shrinkage than xylol. Therefore, transfer the tissue from 

 100 per cent alcohol to a mixture of equal parts of 100 per cent 

 and xylol for a certain period (one hour) ; then change to pin-e xylol 

 for one to two hours; then pure xylol and paraffin for a similar period. 

 If the paraffin used has a melting-point of 50'' to 52° C, then the 

 mixture of xylol and paraffin must be kept at a temperature not far 

 below this to keep the mixture in solution and so enable it to dift'use 

 all through the tissue. It should be remembered that there must 

 be no trace of water left in the tissue. So far it is infiltrated with a 

 mixture of one-half xylol and one-half paraffin. 



This mixture is discarded and the bottle is filled with pure melted 

 paraflSn at a temperature just above its melting-point, i. e., 55° C. 

 In order to maintain the paraffin in a liquid condition, the supply 

 of melted paraffin and the specimen bottles containing tissues 

 being embedded are kept in a constant temperature oven, sometimes 

 called a paraffin oven. After a certain length of time (one hour) 

 the first supply of paraflin is discarded and rei)laced with fresh 

 paraffin and ])laced l)ack in the oven for another hour. It is essential 

 to remove all traces of xylol and to have the pure paraffin diffuse 

 all through the tissue. It is even advisable to change the paraffin 

 once more for another hoiu- in the oven. 



A pa])er boat or a glass dish (Syracuse dish) coated with glycerin 

 is now filled with pure melted paraffin, and the tissue piece poured 

 with its paraffin or transferred to this dish with warmed forceps or 

 spatula. The tissue piece is quickly and properly oriented with a 

 view to the type of sections to be made later. Then a surface film 

 of solid paraffin is produced by blowing across the top of the dish, 

 and the container is gently immersed in cold water for a time, until 



