MS 33.0 



METAL STAINS 



573 



rinse it, place it in the reduced silver solu- 

 tion for four minutes, rinse it again, and 

 transfer it in its turn to the fornuildehyde. 

 If this section does not then turn grey, 

 repeat the process with another section, 

 leaving it in the reduced silver solution 

 for five minutes. Ry this method one may 

 establish the period of time necessary to 

 secure adequate impregnation of sections 

 in tlie particular batch witli wliicli one is 

 dealing. As soon as this has been estab- 

 lished four or five sections may be taken 

 at a time, placed in the silver, and gently 

 rocked to make sure that some sections do 

 not rest on top of others. Next, the sec- 

 tions are removed all at the same time to 

 the distilled water, in which they are 

 rinsed; and then to the formaldehyde, in 

 which they may be accumulated. The 

 whole batch of sections may thus be 

 passed through stain and accumulated in 

 formaldehyde. 



Now take four more clean dishes. In the 

 first of these place distilled water; in the 

 second, the gold chloride toning solution; 

 in the third, the 5% solution of sodium 

 thiosulfate; and in the fourth, another 

 bath of distilled water. The entire batch 

 of sections is now taken at one time from 

 the formaldehyde, placed in the distilled 

 water, and there rocked gently to and fro. 

 If there are many sections, change the 

 water so as to insure thorough washing. 

 When they have been sufficiently washed, 

 the entire batch is transferred to the next 

 dish containing the gold chloride. In this 

 solution the dull steel-grey of the sections 

 changes to the purphsh-blue-grey of gold- 

 stained material. They should be left until 

 the change is complete — usually within a 

 few minutes. It does not in the least mat- 

 ter if they are left for several hours. 



The sections are next taken all at one 

 time from the gold chloride solution and 

 passed without preliminary washing to the 

 sodium thiosulfate solution. This removes 

 from them the silver salts which may not 

 have been completely replaced by the 

 gold. Four or five minutes is sufficient for 

 this change. The sections should certainly 

 not be left here longer than about ten 

 minutes for there is some risk of removing 

 the stain. After the thiosulfate treatment 

 they are passed to the next dish of dis- 



tilled water, in which they must be rocked 

 back and forth. If anj^ considerable num- 

 ber of sections is included in the batch, 

 this distilled water should be changed 

 once or twice, since it is necessary to re- 

 move all thiosulfate from the sections be- 

 fore mounting them. Now take an entirely 

 new batch of dishes containing the cus- 

 tomary dehydrating and clearing agents, 

 run the sections through, and mount them 

 in halsan:i. 



This technique may be modified to show 

 astrocytes, and thus present a very com- 

 plete picture of the supporting structures 

 of the cortex of the cerebrum. Simply 

 leave the sections too long in the silver 

 stain. This will result in a less clear pic- 

 ture of the oligodendria and microglia, but 

 may be desirable for class demonstration 

 purposes. To achieve this result leave 

 them in the silver staining solution until 

 they have changed to a definite dark straw 

 color. This will usuall}' require from five to 

 ten minutes, and may be judged by eye 

 without difficulty. The rest of the process 

 is in every way similar. If the reader is 

 trying this technique for the first time, it 

 might be of interest for him to leave two 

 or three sections in the silver stain while 

 he is taking the remainder through the 

 test of the technique. 



Demonstration of microglia by the 



technique of del Rio-Hortega 



1921b 



The last example demonstrated the use 

 of del Rfo-Hortega's silver-carbonate tech- 

 nique for the demonstration of both oligo- 

 dendroglia and microdendroglia. The pres- 

 ent method demonstrates the use of del 

 RIo-Hortegu's silver-hydroxide technique 

 for a differential demonstration of micro- 

 glia. The technique is much quicker and 

 shorter than that of Penfield and is to be 

 recommended where the demonstration of 

 oligodendroglia is not required. 



The procedure of securing the blocks of 

 tissue and fixing them in Cajal's formal- 

 dehyde ammonium-bromide mixture is 

 identical with that of the last example, to 

 which reference should be made. Pieces of 

 tissue, however, are fixed in a slightly dif- 

 ferent manner. Thev are allowed to remain 



