310 HELEN DEAN KING 



THE HISTOLOGICAL EFFECTS OF FORMALDEHYDE ON THE BRAIN 

 OF THE ALBINO RAT 



The histological changes produced in the cell structures of the 

 brain of the albino rat by various formaldehyde solutions have 

 been described in a previous paper (King '10). In general, as 

 therein stated, such solutions ''give a good fixation of the cell 

 body, but they tend to produce a swelling of the nucleus which 

 is usually accompanied by a poor preservation of the nuclear 

 contents." In order to determine whether the conditions which 

 so appreciably affect the amount of swelling of brain tissue in 

 4 per cent formaldehyde also produce histological changes in the 

 cell structures, preparation.s were made of some of the brains of 

 100-day-old rats used in the experiments described above. After 

 their final weighing at the end of a stated period, these brains 

 were transferred into alcohol and imbedded and stained in the 

 manner recommended in a previous paper (King '10). A careful 

 examination was then made of the large cells in the cerebral 

 cortex at the level of the optic chiasma. 



In a brain that had been subjected to the action of 40 cc. 

 of a neutralized solution of formaldehyde for four weeks the cell 

 outlines were clearly defined, but somewhat irregular; the nuclei, 

 however, were greatly distended and the nuclear contents were 

 badly preserved. In many cases, also, the cytoplasm appeared 

 vacuolated. In a brain kept in 40 cc. of a non-neutralized solu- 

 tion for four weeks, the nuclei appeared fully as much swollen 

 as in the previous case, but the chromatin contents were far 

 better preserved; the cell outlines stained more sharply and were 

 somewhat more regular; and the cytoplasm was not vacuolated. 

 Where the amount of solution used was reduced to 20 cc, the 

 fixation of the cell structures, both in the brain that had been 

 kept in a neutralized solution and in the one that had been sub- 

 jected to the action of a slightly acid solution, the fixation of the 

 cells was about the same as when double the amount of solu- 

 tion had been used. For histological preparations of brain struc- 

 ture, therefore, a neutralized solution of formaldehyde does not, 

 apparently, have the advantage claimed by Bay on, for it greatly 



