94 THE AMERICAN MONTHLY [Apr 



cent solution. Since then I have been carrying on some 

 experiments hoping to find whether or not formaldehyde 

 could be used for such purposes, and if so, what was the 

 best formula to use. 



The formula which has yielded the most satisfactory 

 results for all tissues is as follows ; 



Formaldehyde 40 percent solution 50 cc. 



Distilled Water 50 cc. 



Glacial Acetic Acid 5 cc. 



The principal requisites for any successful fixing solu- 

 tion are that it shall kill and fix the tissues just as quick- 

 ly as possible, and at the same time it must not shrink 

 the cells of the tissues. Another desirable quality in 

 such a solution is that it be of such a nature that it may 

 be removed as quickly as possible preparatory to the de- 

 hydration. All these conditions formaldehyde when used 

 alone fulfills very satisfactorily, and it is especially true 

 of the solution as given above. 



I am aware that previous to this time formaldehyde 

 has been in use as a killing and fixing agent, but so far 

 as I can learn, never in solution stronger than ten per cent. 

 It has also been used in the same solution with mercuric 

 chloride but my experiments convince me that the pres- 

 ence of the mercuric chloride is not necessary ; on the 

 contrary, just as satisfactory results can be obtained from 

 the formaldehyde alone. The solution of the strength 

 given in the formula above has produced no ill effects 

 upon any normal tissues with the single exception of the 

 spinal cord, where the axis cylinder of the fibers seems to 

 be damaged while the cells within the gray matter are left 

 in perfect condition. 



Tissues are killed and perfectly fixed by this solution 

 in from six to twelve hours, though it seems to do them 

 no damage if left in as long as twenty-four hours ; from 

 the fixing solution the tissues are kept about an hour in 

 50 per cent alcohol, from which they are placed from fif- 



