ZOOLOaY AND BOTANY, MICKOSCOPy, ETC. 837 



preserve it there it is only necessary to brush over the surface a layer of 

 thin celloidin. 



(3) Staining of the series. — The arrangement of unstained sections 

 or of very small objects may be facilitated by adding to the bergamot oil 

 a few drops of an alcoholic solution of safranin. The sections stained 

 rose-colour are then easily visible. This staining of the celloidin dis- 

 appears in a day or two, and in a few hours after exposure to sunlight. 

 If now the series, which is placed on a slide, and from which the oil has 

 been mopped up, is to be stained, the slide is placed in a capsule, on the 

 bottom of which are a few drops of ether and absolute alcohol. The 

 series clears up at once, and the celloidin is so far softened that it cleaves 

 firmly to the slide. As soon as drops of ether and of absolute alcohol 

 appear on the slide, it is at once removed to another capsule containing 

 90 per cent, spirit, whereby the celloidin is hardened, and all trace of 

 the bergamot oil removed. After a quarter of an hour the slide may 

 be placed in any stain which is free from water or contains at least 70 per 

 cent, spirit. If aqueous staining solutions are to be used, care must be 

 taken that when exposed to the alcohol-ether vapour the celloidin sections 

 overlap, or at least touch, so that the series may be treated as one large 

 section. 



(4) Applying direction-lines to the celloidin block. — As a general 

 rule, the sides of the block suffice as direction-lines, provided that the 

 celloidin is distinguishable from the outline of the object. This dis* 

 tinction may be rendered more evident by adding to the fluid celloidin 

 or to the bergamot oil a few drops of some pigment dissolved in 90 per 

 cent, spirit, such as picric acid or carmine, dyes which stain celloidin 

 much more quickly than the object. 



If it be necessary that the position of an object should be very accu- 

 rately determined, it is better to imbed in the celloidin a thin plate of 

 gelatin and to arrange the object upon this. By this means there is in 

 each section a fixed outline wirh fixed end-points, and for the purposes of 

 plastic reconstruction leaves li'ttle to be desired as regards orientation. 



(5) Modification of the method of staining with heematoxylin and the 

 chromic acid salts. — The author finds that a modification of Haidenhain's 

 method for staining celloidin series prevents the sections from becoming 

 overstained and brittle. He now uses hsematoxylin and the chromic salt 

 in 1 per cent, solutions in 70-80 per cent, spirit. The bichromate 

 solution is made by mixing 1 part of a 5 per cent, solution of bichro- 

 mate of potash with 4 parts of 80-90 per cent, spirit. Not only must 

 the solution be kept in the dark, but the object must be stained, treated 

 with alcohol, and imbedded in the dark. 



Bruce's Microtome for cutting whole sections of the Brain and 

 other organs. — This instrument (fig. 153) was designed by Dr. A. Bruce 

 to meet the requirements of those who wish to cut sections of 4 in. 

 diameter and upwards. The construction was necessitated by the incon- 

 veniences which were foimd to attach to large microtomes made after the 

 manner of Eutherford's microtome. The method of freezing adopted in 

 Rutherford's instrument is well adapted for freezing tissues of moderate 

 size, where the freezing mixture is at a small distance from the tissue, 

 but is quite unsuited for a tissue of 4 or 5 in. diam., where some part 

 of the object to be frozen would be at least 2^ in. from the freezing 

 mixture. 



In the new instrument freezing is effected by laying the object to be 

 1888. 3 "l 



