IMBEDDING MKTflODS (PARAFFIN). 103 



The objects having been mounted on the carrier of the 

 microtome in position for cutting, pare the blocks to the 

 proper shape (see below, " Cutting ") and sufficiently close 

 down to the objects, and go round them with a lens. If any 

 bubbles or cavities or opaque spots be present, prick with a 

 heated needle till all is smooth and homogeneous. Minutes 

 spent in this way are well invested. 



It is said by some workers that it is well to cut within a 

 few hours of imbedding if the structure be at all delicate, as 

 paraffin may continue to crystallise slowly to a certain extent 

 even after rapid cooling. But this danger is very greatly 

 diminished if the mass have been properly cooled. And 

 according to my experience the damage likely to arise from 

 the crystallisation of the paraffin has been greatly exaggerated. 

 As stated in 3, I find no better medium for the preserva- 

 tion of tissues than paraffin. 



133. Orientation of the Object. The above-described manipulations 

 of definitive imbedding are in most cases sufficient. But it may be desir- 

 able to have the object fixed in the cooled block in a more precisely- 

 arranged position, and, above all, in a more precisely-marked position, than 

 is possible by these simple methods. Here is a method due to PATTEN 

 (Zeit.f. wiss. Mik., xi, 1, 1894, p. 13), which is especially useful when one 

 desires to orient accurately large numbers of small and similar objects. 

 You get some writing paper of the soil that is made with two sets of raised 

 parallel lines running at right angles to each other (according to WOOD- 

 WOBTH. see below, this is known as " linen cloth paper "). Small strips 

 are cut from this, and at suitable intervals along them small drops of a 

 mixture of collodion and clove oil, of about the consistency of thick honey, 

 are arranged close together along one of the ribs that run lengthwise. The 

 objects to be imbedded are cleared in clove oil or oil of bergamot not 

 turpentine. They are taken one by one on the point of a knife, and after 

 the excess of oil has been drawn off are transferred each to a drop of the 

 collodion mixture. They may be adjusted therein under the dissecting 

 microscope, and will stay in any required position. When half a dozen or 

 more objects have been oriented in reference to the cross lines (which are 

 to be parallel to the section planes) the whole thing is placed in turpentine. 

 This washes out the clove oil and fixes the objects very firmly to the paper. 

 The paper with the attached objects is now passed through the bath of 

 paraffin and imbedded in the usual way. After cooling on water the block 

 is trimmed and the paper peeled off, leaving the objects in the paraffin 

 close to the under surface of the block. This surface is now seen to be 

 marked by the orienting lines of the ribbed paper, and also by any record 

 numbers which may before imbedding have been written with a soft pencil 

 on the paper. 



