34 STUDENTS HISTOLOGY. 



longest time. For ganglion-cells the time should be intermediate 

 between these. 



b. The tissue is placed in a three -fourths per cent, solution of 

 nitrate of silver for one to six days. 



c. Cut rather thick sections, about 50 p. Alcohol is to be used 

 as little as possible. Sections may be cut free-hand or between 

 pieces of elder -pith, or by fastening on the block with paraffin 

 (page 18); or by imbedding rapidly in celloidin, taking about 

 twenty minutes for all the steps. 



d. Alcohol, xylol, and balsam, as usual. 



e. Mount without a cover -glass, and keep in the dark. 



COX'S MODIFICATION OF THE GOLGI METHOD 



Golgi found that the bichloride of mercury could be used for 

 the impregnation of nervous tissues in much the same manner as 

 the nitrate of silver. The formula proposed by Cox has been 

 highly recomended. 



Bichromate of potassium (five per. cent. solution) 20 parts. 

 Bichloride of mercury (five per cent, solution) . . 20 parts. 

 Simple chromate of potassium (five per cent, sol.) 16 parts. 

 Distilled water 30 to 40 parts. 



Specimens should be left in the mixture for one month in sum- 

 mer, and for two to three months in winter. The impregnation 

 should take place uniformly throughout the preparation. 



INJECTION OF BLOOD-VESSELS 



To make the small blood-vessels appear in microscopical prep- 

 arations they may be filled with some colored substance. An 

 entire animal recently killed, or merely one organ, may be injected. 

 A canula is tied in the proper vessel and injected with a syringe, or 

 from a flask holding the coloring substance, which is emptied by 

 mercurial or water pressure. Among many formulas for injecting 

 fluids, the following may be used: 



Soluble Berlin blue . . 3 grams. 



Water 600 c.c. 



This mixture has the advantage that it may be used cold. 

 CARMINE-GELATIN must be kept warm while injection is pro- 

 ceeding, as must the object which is being injected. Two and one- 



