8 ATLAS OF NERVE CELLS 



upon the slide, if it be desired to mount them serially as described below, is being placed 

 in position, the film of celloidin will dry sufficiently. Alcohol can then be applied and the 

 next section cut. 



For clearing, oleum origani cretici is preferred. It clears readily from 95 % alcohol, 

 does not make the sections brittle, and sections may be kept in it for a considerable time, 

 even a day or so, without injury. It is better before mounting to wash them briefly in xylol. 

 The xylol allows the balsam to set more rapidly, and is less liable to affect the preparations 

 than is the origanum brought over into the balsam with the section. On the other hand, 

 xylol tends to make the sections crumpled and brittle. 



In the handling and mounting, several methods may be employed. The sections may be 

 brought from the origanum upon the slide, the oil blotted off, and a drop of balsam placed 

 upon the section, the mount then being watched to see that the balsam does not run off. 

 This has the disadvantage that a small quantity of origanum remains in the section, usually 

 not enough to prevent the balsam from drying properly. Another mode of procedure is 

 to bring the sections from origanum into xylol, and thence into a dish of balsam. The 

 diffusion of balsam takes place while in this, and consequently when the section is lifted out 

 and placed upon the slide, the balsam does not tend to run off. The disadvantage here is 

 that sections of the central nervous system tend to become crumpled and brittle. 



The best method, one which preserves the sections in serial order, and keeps them flat 

 for photographing, is the following. The sections are brought from the knife and arranged 

 on the slide in 95 % alcohol, and, after the slide is filled, the alcohol is blotted off and a 

 thin solution of celloidin is quickly run over the slide and drained off. After the film has 

 set by slightly drying, absolute alcohol is quickly run over the slide and drained off, thereby 

 facilitating the subsequent clearing. Care must be taken not to dissolve the film. The slide 

 is then immediately placed in origanum, where it may remain while the next slide is being 

 filled. It is then placed successively in two dishes of xylol to remove the origanum. If the 

 slide clouds up in xylol, it has not been completely dehydrated. Absolute alcohol may then 

 be again run over the slide, which may then be again cleared in origanum. A slight opacity 

 outside the sections will usually clear up after mounting. For the mounting medium a solu- 

 tion of damar in xylol is used. 



The sections are mounted without a cover slip, and to do this properly is not as simple 

 as would at first sight appear. The sections should be covered with a layer of balsam, which, 

 when dry, should be even and as thin as possible and yet cover the sections. If a thin 

 layer be applied at first, it runs off in spots, leaving the sections dry, and requiring constant 

 watching, which interferes with other work. All this may be obviated by placing the slide, 



