ANATOMICAL TECHNIQUE 449 



of small pieces in a vessel covered with gauze or cheesecloth to 

 prevent the loss of material. Larger pieces of wood, particularly 

 when they are heavy, can be washed in open bottles. 



The next stage in the process of preparation for sectioning 

 depends on the nature of the material. If the objects are very 

 small, and especially if they lack homogeneity on account of the 

 presence of soft as well as hard tissues, they must be subjected 

 to imbedding in nitrocellulose or paraffin, and the former process 

 is ordinarily preferable. In the case of larger objects one of two 

 conditions may present itself. Either the structure is quite homo- 

 geneous, as in peachstones, cubes of oak wood, etc., or else it con- 

 sists of tissues both hard and soft, as, for example, segments of 

 stems or roots. In blocks of uniform texture, after washing is 

 complete, a transfer is effected to a fluid consisting of equal parts 

 of alcohol of 30 per cent strength and glycerin. Immersion for 

 some days in this reagent fits the material for cutting. When the 

 objects are of some size and are not of homogeneous organization 

 they are run up through alcohols after washing to a strong or 95 

 per cent solution. This is changed twice and the material is then 

 placed in equal parts of strong alcohol (95 per cent) and glycerin. 

 A week or more is needed under these circumstances to bring about 

 a consistency suitable for sectioning. 



IMBEDDING IN NITROCELLULOSE 



When the material is unhomogeneous and is in small pieces, 

 it must be imbedded in nitrocellulose. There are a number of 

 different types of nitrocelluloses which may be employed. On 

 the whole, the best for the purpose is Schering's celloidin. This 

 is a special preparation of particular toughness, solubility, and 

 purity. When extreme transparency is a desideratum, the nitro- 

 body known as photoxylin may be used. In general, however, 

 a nitrocellulose which is entirely transparent is quite unnecessary, 

 since all are sufficiently translucent to permit the ready orienta- 

 tion of the object in cutting. The cheapest and most readily pro- 

 curable nitrocellulose is photographic guncotton prepared for 

 making the so-called "wet-plates" used in certain photomechani- 

 cal processes. This is inexpensive and may be purchased at any 



