1902] MICROSOCOPICAL JOURNAL. 29 
generally recognized by users of the microscope. This 
process of impregnation may last for two months. In 
the case of the retina and optic nerve this method has 
yielded pictures which are astonishingly complete. The 
cells are revealed even to their finest processes and ap- 
pear as if drawn diagramatically. Some of the drugs 
used in impregnation are bichromate and corrosive sub- 
limate; bichromate and nitrate of silver; bichromate of 
potash, osmic acid and nitrate of silver. Osmic acid is 
costly which has led to the substitution of formalin in 
many cases. 
Golgi discovered this impregnation but Cajal] discover- 
ed a double impregnation. Golgi’s method is best ap- 
plied to the delicate neuroglia cells of the optic nerve 
which cells it demonstrates perfectly. Cajal’s method is 
used on the retina which yields beautiful pictures. He 
soaks small pieces (5 mm. in dia.), for three days, in 
formalin and bichromate of potash, then, for three days 
more, in rather less than one per cent solution of nitrate 
of silver. 
Endothelium, nervous plexuses and ganglion cells are 
| beautifully demonstrated by the Intra Vitam Methylene 
blue method. This was started by Ehrlich and has been 
improved by Kallius, Apathy, Bethe and especially by 
Dogiel. It is complicated and requires wit and skill but 
yields the grandest of results. 
_ For the injecting of blood vessels with coloring mat- 
ter as soon as an animal has died by bleeding, there are 
now two very useful ‘‘masses.” The red consists of warm 
gelatine-carmine which by the addition of acetic acid 
changes the cherry-red to a brick-red opaque tint. The 
blue mass involves four solutions: sulphate of iron, prus- 
siate of potash, oxalic acid and gelatine. A deep blue 
stain is obtained thereby. If only the eye is to be in- 
jected, it can be done by puncturing with a hypodermic 
syringe charged with Berlin blue. If used upon the 
