THE HISTOLOGICAL TECHNIQUE 9 



after being brought from xylol, on a level table and flooding it with as much of a rather 

 thick solution of damar as it will hold without overflowing. It can then be covered over 

 so as to protect it from dust, and left at least half an hour and longer if convenient. Dif- 

 fusion of the balsam into the celloidin and sections will then be completed, and the superflu- 

 ous balsam may be drained back into the bottle. Just how much to leave on the slide 

 depends upon the thickness of the balsam and must be determined by experience. After 

 the superfluous balsam has been removed, the slides are put in an oven (5O-55 C.) over night 

 to harden the balsam. One of the essentials to a good preservation of preparations, to avoid 

 yellowing, etc., is that the balsam be quickly and completely hardened. 



Besides the rapid method, certain of the preparations were made either by means of 

 Golgi's mixed method or by means of what might be termed modifications of Golgi's long 

 method, introduced by the writer. 



Plates III., V., and VI. are taken from preparations made by means of Golgi's mixed 

 method. Here the cord was placed in Miiller's fluid (potassium bichromate alone answers 

 as well) for one week, then for several days in osmic-bichromate, and finally in silver nitrate. 

 This method was not used very extensively. It appears to be especially adapted to bringing 

 out the cells rather than the fine plexus of fibres, and is particularly applicable to adult 

 tissue. Cajal recommends it especially for the demonstration of the cells and transverse 

 fibres of the molecular layer of the cerebellum in young mammalia. It was the method 

 most strongly recommended by Golgi himself. This method, furthermore, permits the tissue to 

 be kept, as Golgi points out, for from two to thirty days in bichromate, from which, at con- 

 venient times, pieces can be removed and placed into osmic-bichromate and thence into silver 

 nitrate. Whether this could equal the rapid method with embryonic material has perhaps 

 been hardly sufficiently tested, but the quick fixation of the rapid method would appear to 

 be especially desirable with the more delicate and less firm embryonic tissue. 



The long Golgi method has not been employed in preparations shown in this Atlas. 

 The impregnations made by the long method differ from those made by the rapid method in 

 the fact that they possess greater stability in strong alcohol, in which they may remain for a 

 considerable period without deterioration. The method is especially indicated for the adult 

 cerebrum and cerebellum, but one of the two modifications given below is probably easier. 



It has been found by the writer that lithium bichromate hardens tissue much more 

 rapidly than the potassium salt, and, by employing the former, the period of hardening may 

 be cut down to a few days. 



Since the introduction of formalin for hardening, Hoyer, Jr., discovered that material kept 

 in it could be afterwards impregnated like fresh material, and that the osmic acid could in 



