On Cajal's Formalin- Silver Nitrate Impregnation Method. 325 



3. Differentiate partially in 90 p.c. alcohol ; pass through 

 absolute into — 



4. Clove oil. Complete differentiation in this, 



5. Xvlol. ]\Iount in balsam. 



It is advisable to rinse the xylol after the clove oil, otherwise 

 the sections may fade. 



General Precautions. — The Cajal method is somewhat capricious, 

 and it is often difficult to determine the cause of failure. Thus, if 

 a number of pieces of the same tissue, equal in size, be treated 

 together the impregnation will often be good in some and bad in 

 others. Hence the advisability of embedding several pieces of 

 tissue in the same block. 



Generally speaking, the outer layers of the material are over- 

 impregnated, while the central portion may not be impregnated at 

 all. The intermediate zone is usually the best. 



Every dijSerent tissue and different animal has its optimum 

 times for fixation and silvering which have to be worked out for 

 each individual case. This applies especially to Invertebrates. 



It is, in my experience, immaterial whether the silvering 

 process takes place in the light or dark. Tissues should be fresh, 

 as autolysis of the Golgi apparatus occurs soon after death, 



4. Impregnation of Elements other than the Golgi 

 Apparatus by Cajal's Method, 



In addition to a black impregnation of the Golgi apparatus and 

 the staining of the ground cytoplasm yellow, other elements may 

 be affected. Thus mitochondria are often impregnated golden to 

 dark brown, while collagen connective tissue fibres may go brown 

 to black. 



Further, the following intracellular elements have been 

 described as being impregnated by Del Eio Hortega : — 



(a) A spiral filament, apparently wrapped around the nuclei 

 of unstriated muscle fibres {12). 



(b) The myofibrillse in the same tissue {Hid.). 



(c) Several structures {11) within the nuclei of ovarian egg- 

 cells in various Mammals, viz. (i.) a small spiral rod apparently 

 lying free within the nucleus ; (ii,) within the nucleoli several 

 small bodies either round or in the form of stumpy rods ; (iii.) a 

 fine intranuclear network identified as linin by Del Eio Hortega. 



The relationship (if any) between these elements associated 

 with the nucleus has yet to be determined, 



5, Utility of the Cajal Method. 



The application of this method has yielded very interesting 

 results in the hands of Histologists, Cajal has thereby demon- 

 strated a Golgi apparatus in the cells of nearly all Mammalian 



