Note on GarhoUc Acid as a Fixative for Histological Preparations. 171 
l)acteriological work, its remarkable power of fixing and preserving tissues 
for examination under the microscope have not been appreciated, and, if 
we except the fixative of Pappenheim, in which indeed it is mixed with 
corrosive sublimate, has not been made use of. 
As an antiseptic and preservative Kaiser adds 1*0 carbolic acid to lOO'O 
gelatine for imbedding, and added to saccharine solution or glycerine jelly 
it is used for mounting sections. 
Weigert uses carbolic-xylol to clear celloidin sections, and it has been 
mixed with cedar and other oils to act as a clearing agent. Moreover, it is 
used for dehydrating sections. 
Its principal use in microscopy, however, has been as an addition to 
various aniline dyes to facilitate the staining especially of bacteria, as in the 
well-known stains, carbol-fuchsin and carbol-methylene-blue, etc. 
A solution is easily prepared from Calvert's carbolic acid (I generally use 
No. 1) or from phenol. The crystals are melted by placing the bottle 
containing the carbolic in boiling water. Liquefaction quickly takes place. 
The desired quantity can be readily poured out and measured. 
Carbolic acid acts best in 5 per cent, solutions ; any lower percentage 
gives unsatisfactory results. 
The preparation to be fixed, preferably small, is left in the fluid from 
three to six hours ; smaller pieces of tissue do not require so long. I have 
had excellent results with a two hours' fixation, but no harm is done by 
leaving it longer than six hours in the fluid. 
As carbolic acid is freely absorbed by the tissues, the amount of the 
fluid used must be liberal. 
Subsequent washing out is not needed, and the after-treatment follows 
the usual course — dehydration in the customary manner and clearing by 
scylol, or preferably by cedar oil, before imbedding. 
Briefly, the advantages of carbolic acid as a fixative are : 
(1) Rapid penetration and efiicient fixation with the least distortion or 
.alteration of tissue. 
(2) Grood optical differentiation, all cell structures as well as the cell 
wall remaining well and clearly defined. 
(3) The readiness with which good staining is obtained after fixation by 
this method. 
Literature. 
Ehrlich. — ' Encyklopadie d. Mikroskopischen Teclmik/ 1910, and article Carbol 
saure. 
CusHNT. — 'Text-book of Pharmacology/ 1910. 
GoDLEE. — ' Life of Lord Lister.' 
Lee.— ' TheJMicrotomist's Vade-mecum/ seventh edition, 1913. 
