COLLODION AND OTHER IMBEDDING METHODS. 121 



recently introduced practice of clearing before cutting, and 

 cutting dry as described in 165. 



151. Collodion, Celloidin, and Photoxylin. The collodion 

 method is due to DDVAL (Journ. de VAnat., 1879, p. 185). 



Celloidin, recommended later on by MERKEL and SCHIEFFER- 

 DECKER (Arch. f. Anat. u. Phys., 1882, p. 200), is merely a 

 patent collodion. It may be obtained from GRUBLER, or the 

 other dealers in histological reagents. It is sent out in the 

 form of tablets of a tough gelatinous consistency and slightly 

 milky- white transparency. These tablets may, if desired, be 

 dissolved at once in ether, or a mixture of ether and alcohol, 

 to make a collodion of any desired strength. But it is 

 better, as recommended by APATHY, to cut them up into thin 

 shavings, which should be allowed to dry in the air until they 

 become yellow, transparent, and of a horny consistency, and 

 that these be then dissolved in alcohol and ether (sulphuric, 

 free from acid) . The solutions thus prepared are free from 

 the excess of water that is present in the undried celloidin, 

 and give after hardening a mass that is more transparent and 

 of a better consistency for cutting (Zeit. f. iviss. Mik., vi, 2, 

 1889, p. 1(34). 



Imbedding masses of excellent quality can be prepared 

 with ordinary collodion, but celloidin furnishes more readily 

 solutions of known concentration. Otherwise there is but 

 little to choose between the two, and therefore in this work 

 the terms collodion and celloidin are used indifferently. 



Photoxylin (KBYSINSKY, VIBCHOW'S Archiv, cviii, 1887, p. 217 ; BUSSE, 

 Zeit. f. wiss. Mile., ix, 1, 1892, p. 47) is a dry substance, of the aspect of 

 cotton wool, and chemically nearly related to celloidin. It can be obtained 

 from GRUBLER. It gives a clear solution in a mixture of equal parts of 

 ether and absolute alcohol, and should be used in exactly the same way as 

 celloidin. It has the advantage of affording a mass which after hardening 

 in 85 per cent, alcohol remains perfectly transparent. But celloidin or 

 common collodion also give perfectly transparent masses if cleared in bulk 

 as I recommend should be done ( 163 165) ; so that there is no advan- 

 tage on this head in having recourse to photoxylin, unless it be desired to 

 proceed in the old way. Some writers say that it gives a better consistency, 

 but others deny this (APATHY, e.g.). 



152. Preparation of Objects. The objects must first be very 

 thoroughly dehydrated with absolute alcohol. They are then 



