CH. XI] PREPARATIONS BY THE COLLODION METHOD 391 



After half an hour or longer the preparation is ready to stain. 



635. The castor-xylene method of sectioning. The prepara- 

 tion of the tissue is the same as described in 625-629, except that 

 when the collodion is hardened in chloroform it is transferred, not to 

 alcohol, but the block is placed in castor-xylene ( 554). In a few 

 days the collodion gets as transparent as glass and one can see the 

 tissue within with great clearness. It can remain in the castor- 

 xylene indefinitely. 



In cutting one proceeds exactly as in 632, except that the block 

 is kept wet with castor-xylene and not with alcohol. The sections 

 are arranged on the knife and transferred to the slide in the same way 

 'as for alcohol sectioning ( 633-634). 



For fastening the sections to the slide, as no water is present, one 

 can add the ether alcohol at once. It is advantageous here to have 

 a mixture of ether two parts and absolute alcohol one part for melt- 

 ing the collodion in these oil sections. 



Allow the slide to remain in the air till the collodion begins to look 

 dull ; then the slide may be transferred to a jar of xylene to remove 

 the oil. From the xylene it is transferred to 95 % alcohol and then 

 the slide is ready to be stained, etc., as described below ( 638). 



636. Steps in order for the collodion method. 



Name 



No. 



DOUBLE IMBEDDING IN COLLODION AND PARAFFIN 



637. Need of double imbedding. Some objects like ova with 

 considerable yolk and other objects in which the different parts are 

 of unequal density or very loosely bound together are advantageously 



