22 STUDENTS HISTOLOGY 



The portions of tissue should be not more than one -half to one 

 centimeter thick. 



Alcohol is the most generally used of all hardening and fixing 

 fluids. Tissues preserved in it will keep indefinitely, especially if 

 the strong alcohol be replaced by eighty per cent, alcohol after a 

 time. When bacteria are to be demonstrated in the organs, alcohol 

 is as good as any agent that can be used. But when the blood, 

 the nuclear figures, the elements of the nervous system, and the 

 finer points in histological structure are to be studied, other fluids 

 are more suitable. 



MULLER'S FLUID 



Bichromate of potassium 2.5 grams. 



Sulphate of sodium 1 gram. 



Water 100 c.c. 



Miiller's fluid is one of the most valuable of all fixing agents. 

 The time required for hardening is six weeks or more, but harden- 

 ing may be hastened by placing the jar in an incubator. The 

 pieces of tissue must be small. The fluid must not become dis- 

 colored, and must be changed frequently at first. It is most 

 valuable for nervous tissues, which harden only after months. 

 After hardening, the tissues must be washed in running water for 

 twenty -four hours, and are then placed in alcohol, except nervous 

 tissues, which are placed in strong alcohol without washing, 

 when the Weigert haematoxylin stain is to be used. Miiller's 

 fluid preserves the blood - corpuscles in the organs admirably. 

 The hardening can be hastened by adding ten per cent, of 

 formaldehyde (forty per cent, solution). This mixture is known 

 as ORTH'S FLUID. ' It has the advantages of Miiller's fluid, while 

 the hardening is completed in a week or less. 



FORMALDEHYDE is a gas which is manufactured in a forty per 

 cent, solution in water. The solution has a very pungent and 

 irritating odor, and is a powerful germicide. It is most valuable 

 for preserving large anatomical and pathological specimens, which 

 keep their natural colors in it much better than in alcohol. It is 

 also useful in histological work as a fixing agent. Pieces of tissue 

 one centimeter thick are hardened in twenty -four hours in ten 

 parts of the forty per cent, formaldehyde solution of commerce, and 

 ninety parts of water. Very small pieces of tissue may be 

 hardened in formaldehyde for a few hours, and excellent sections 



