70 A RESUME OF THE USES OF FORMALIN. 



two per cent, solution of formalin gave nearly perfect results. 

 Sheep's brains hardened in this mixture retained their original 

 colour and form, and were very little increased in volume. " A 

 brain that before treatment (June 20th) measured one hundred 

 and one cubic centimetres, when finally prepared (July 15th) 

 measured one hundred and three cubic centimetres." 



Fish states that an excellent hardening of the brain may be 

 obtained with the following mixture : 



Water ... ... ... ... 2,000 c.c. 



Formalin ... ... ... 50 „ 



Sodium chloride ... ... ... 100 grms. 



Zinc chloride ... ... ... 15 n 



The specific gravity should be about i"05. The brain is left 

 in this mixture for a week or ten days. The blood-vessels and 

 cavities should be injected with the fluid if possible. After the 

 end of the ten days the brain is transferred to formalin, fifty cubic 

 centimetres, and water, two thousand cubic centimetres, where it 

 may be kept indefinitely ; or, after being a week in this fluid, it may 

 first be transferred to fifty per cent., then to ninety per cent., and 

 finally to ninety-five per cent, alcohol. He has also treated por- 

 tions of the adult central nervous system by this method, and 

 afterwards with mercuric chloride, picro-aceto-sublimate, and 

 chromacetic-acid mixtures, with good results. 



For hardening eyes Leber used formalin mixed with water in 

 the proportion of one to ten. The natural colour and transparency 

 of the organ were retained. The cornea and lens became but 

 slightly cloudy. In his opinion, the fine structure was as well 

 preserved as with Miiller's fluid. If the eyes were placed in alcohol 

 the cornea and lens became opaque. I have employed formalin 

 in a five per cent, solution for this purpose with the same results. 

 As a hardening agent for microscopic work, formalin has been 

 used very extensively, the strength of the solutions employed 

 varying from one per cent, to the full strength — forty per cent. 

 As the results of many observations, it may now be said, with 

 possibly one or two exceptions, that formalin alone is an unfit 

 reagent for hardening tissues for microscopic work. It was con- 

 demned by Hermann in 1893 ; Lachi states that it has an injurious 



