The Microscope. 135 



the bath and placed in soft paraffine, in which it is kept at a tem- 

 perature of 57° to 59° for a few hours ; it is soaked next in the hard 

 paraffine mixture for about the same time or a little longer. It is 

 very important that the temperature should not reach 60°. The actual 

 process of imbedding takes place according to the well known 

 methods. After the block is hardened in which the object is 

 imbedded it is trimmed down into the proper shape, two of its surfaces 

 are made carefully parallel, these are the two which are subsequently 

 to be placed in the microtome parallel with the cutting edge of the 

 knife. But the trimming of the block must not be completed yet ; 

 the other two sides which need not be parallel, ought not to be cut 

 down until later ; the parallel -sided block is now stuck down in 

 the usual manner on to the object-holder of the microtome, and dipped 

 in melted soft paraffine, so as to be coated completely by it, being 

 held in the soft paraffine for some seconds, so that the surfaces of 

 the block of hard paraffine may be somewhat softened by the high 

 temperature, and so a more perfect adhesion be secured for the coating 

 of the soft paraffine ; the block is withdrawn from its bath and 

 allowed to cool, after which the coat of soft paraffine is carefully cut 

 off on three sides, leaving a coat of soft paraffine only on the side 

 which is to face the knife. If the coat of paraffine is observed care- 

 fully, it will be seen that at the corners of the block it is irregular, 

 but the middle portion of the coat is of quite even thickness, while 

 toward the edges of the block it is irregular in thickness ; if, now, 

 the rest of the trimming of the block is done, these irregular corners 

 will be cut off, and only the even portion of the coat will be left 

 for use in the actual cutting. When the block is clamped in the 

 microtome the surface having the soft paraffine upon it is turned 

 towards the knife ; by adopting this method, it will be found that 

 there usually is no difficulty in obtaining a ribbon of sections, each 

 section adhering perfectly to its predecessor. If this method is 

 used there is much less tendency for the sections to get caught on 

 the blade of the microtome knife during the cutting, as is apt to 

 happen when the block has been left coated on all sides or on two, 

 since in the latter cases some of the soft paraffine gets rubbed on to 

 the blade of the knife and there catches hold of the sections suffi- 

 ciently to hinder the formation of a satisfactory ribbon. In order 

 to get the two edges of the paraffine block exactly parallel, the 

 apparatus devised by Prof. Osborne will be found convenient. 



It is desirable whenever it is possible to color in toto before- 

 hand. The safest staining fluid for this purpose that I have tried 

 seems to be alum cochineal, which penetrates well, so that objects of 



