NEUROGLIA AND SENSE ORGANS 547 



two months of hardening. The capacity for taking the gold 

 disappears first from the protoplasmic, and then from the fibrous, 

 neuroglia. 



We have found that this method can be successfully used on 

 material fixed in formol saline for several weeks or even months. 

 Frozen sections are cut at 20 y, and left in formol bromide at labora- 

 tory temperature overnight. After a quick wash they are 

 then placed in the following solution, which must be freshly 

 prepared : — 



Mercuric chloride . . . . 0-5 to 1-0 grm. 



One per cent, gold chloride (Merck's 



brown, or yellow crystals) . . 20 c.c. 



Distilled water . . . . . 30 ., 



The sections stay in this solution for half an hour or longer in 

 the incubator at 37° C. and are then fixed as in the original Cajal 

 method. Tliis stronger solution will often be found preferable to 

 Cajal's formula. (See also Raileann, Rev. Neurol., i, 1930, 

 p. 1018). 



CoRTEN (Wertham's "The Brain as an Organ," the Macmillan 

 Company, New York, 1934) uses tissue fixed in formol saline. 

 Frozen sections cut at 25 [x are placed in ammonium bromate, 15 

 c.c. ; neutral formalin, 100 c.c. ; distilled water, 400 c.c. ; the 

 solution being heated till it steams. Sections are then transferred 

 to antiformin, 3 c.c. ; distilled water, 2 c.c. ; 96 per cent, alcohol, 

 8 c.c, for six to fifteen seconds. They must be moved about in 

 this solution. After washing in two changes of distilled water 

 sections are treated with Cajal's gold sublimate solution, the use 

 of a higher concentration of mercuric chloride being recommended. 



By means of Cajal's method two categories of neuroglia elements 

 become stained a dark purple on a much lighter purplish back- 

 ground. The first category consists of neuroglia cells provided 

 with a changing number of variously ramified protoplasmic pro- 

 cesses, which inter-cross with those of other cells, and thus give 

 origin to Cajal's pleurigenic plexus. These neuroglia cells prevail 

 in the grey layers of the human cerebral cortex, and form the 

 bulk of the protoplasmic neuroglia (§ 1082). In Cajal's prepara- 

 tions they appear beset with vacuoles, situated both within their 

 cytoplasm and along their processes. The vacuoles or spaces are 

 occupied by granules (gliosotnes), which may be stained either by 

 Cajal's uranium nitrate method (§ 723) (superficial sections) or 

 by methods generally used for the demonstration of mitochondrial 

 formations as well as by the methods of Eisath and Fieandt. 

 The other category of neuroglia elements shown by the gold 

 chloride and sublimate method consists of astrocytes, viz,, of 

 neuroglia cells, also provided with a changing number of pro- 

 cesses, but chiefly characterised by the presence of fibres which, 



18—2 



