626 
PIERRE A. FISH. 
NEUTRAL RED IN HISTOLOGY AND BACTERIOLOGY. 
By Pierre A. Fish, D. Sc.,D.V. S.,N. Y. State Veterinary College, Ithaca, N. Y. 
Neutral red (. Neutralroth , rectif. nach Ehrlich ) in weak so¬ 
lutions of 1-10,000 or thereabouts, has been demonstrated to pos¬ 
sess considerable efficiency in the staining of vital tissues, but 
some difficulty has been experienced in finding a trustworthy 
mordaunt to prevent the dye from washing out of the stained 
tissues too readily. For the study of living protozoa it has 
proven of considerable service, but for higher forms which must 
undergo killing, imbedding and sectioning, there have been 
manifest difficulties encountered. Quite satisfactory results, how¬ 
ever, were obtained in the case of a tapeworm {Dipylidium) found 
in a dog. The living worm after an immersion of 12-15 hours in 
normal salt solution with enough of the neutral red salt to tino-e 
the fluid, became markedly colored but somewhat shrunken 
owing to the difference in the temperature. In order to avoid 
the removal of the dye from the specimen and to prepare the tis¬ 
sue for the subsequent processes some of the segments of the 
worm were immersed in a 3 to 5 per cent, solution of formalin 
also tinged with the dye. After 12-24 hours the tissue was thor- 
oughly fixed and there was no diminution in the color. The 
subsequent treatment was that as ordinarily employed for in toto 
staining. The superfluous stain was removed during the passage 
of the tissue through the alcohols, and the specimen, after dehy¬ 
dration and clarification was mounted in balsam. 
Portions of the vertebrate nervous system have also been 
simultaneously fixed and stained en masse in the formalin-neu¬ 
tral red mixture, and, after imbedding in collodion or paraffin, 
have been sectioned and mounted with very satisfactory results. 
Section staining has also resulted very satisfactorily, if the sec¬ 
tions are treated with absolute alcohol immediately after stain¬ 
ing. With lower percentages of alcohol the color is generally 
all washed out by the time the tissue is dehydrated. The dye 
is also soluble in most of the clarifying reagents, so that in order 
to obtain the best effects the absolute alcohol should be allowed 
