Microscopy. 1039 
The evanescence of the color-reaction is a serious drawback, but 
this difficulty has been met with some success by the use of iodine 
and picro-carmine as “ fixing ” reagents. 
The method of procedure, according to Prof. ©. Arnstein, '! and 
his pupils, Dogiel and Smirnon, is as follows :— 
nject the vena cutanea magna of a frog with 1 ce. of a satu- 
rated solution of methyl-blue. The tongue and palate are at once 
colored, but the coloring substance is confined to the blood-vessels, 
and does not at first affect the nerves. After an hour or two the 
nerves supplying the taste papille appear blue, and at the same time 
the nerve-meshes of the palate are also stained. The motor nerve- 
ends show the stain a little later. The color-reaction only lasts a 
short time, often not more than five to ten minutes. It should be 
fixed at the moment of its greatest intensity. If iodine is used for 
this purpose, proceed as follows: — 
: lace the frog in a 1 per cent. aqueous solution of potassic 
lodide, in which metallic iodine has been dissolved to saturation, 
and inject the blood-vessels with the same solution, thus freeing 
them from the blood as far as possible. 
Next cut out the parts needed and leave them in the iodine 
solution from six to twelve hours. 
Transfer to water and leave until most of the iodine has 
been withdrawn. As the result of this treatment, the nerves will 
have a dark brown or grey color, and the surrounding tissue will 
nearly colorless, 
5. Mount in acidified glycerine. 
Picro-carmine as a “ fixing ” agent, is said to give more dura- 
na preparations than iodine, Bat the latter gives the more intense 
color i 
Mammals and birds die soon after injection of methyl-blue, so 
that a true intra vitam reaction can not be easily obtained. How- 
ever, a very satisfactory reaction may be obtained, with these animals, 
after death from chloroform. The injection may be made from the 
eart or from any blood-vessel. The appearance of i color in the 
nerves can be followed under the microscope, and when its maximum 
has been reached, the fixing reagent applied. r 
Finally, with a dilute solution of methyl-blue, preparations can 
be stained directly on the slide. The retina of fishes, birds, an 
mammals, can be more successfully stained this way than by 
Injection, 
Dr. Max J oseph? has tested Ehrlich’s method on Heteropods and 
found that the clear intra vitam stain could not be satisfactorily 
fixed. He remarks that the commercial methyl-blue is unfit for use, 
, Anat. Anz. ii., 1887, No. 5, p. 125, and No. 17, p. 551. 
Anat. Anz., June, 1888, No. 15, p. 420. 
