68 A RESUME OF THE USES OF FORMALIN. 



of two per cent.,* though weaker solutions, from three-quarters 

 to one per cent., have been used. These weaker solutions are 

 objectionable on account of the likelihood of the growth of moulds, 

 and because they cause more or less swelling of the tissues. As 

 the result of the experience of numerous observers, it appears that 

 five per cent, solutions give better results. 



The quantity of the solution should be large — a hundred times 

 the volume of the specimen — and the fluid should be renewed at 

 the end of twenty-four hours. In some cases it is well to renew 

 the fluid a second or even a third time. Formalin used in this 

 manner preserves the natural form, the transparency, and, to a 

 certain extent, the natural colour of the specimens. In some 

 specimens the blood-colour appears to be bleached out, but if the 

 preparation is placed in strong alcohol this is nearly, if not entirely, 

 restored. For preserving the blood-colour of specimens, Johres 

 makes use of the following procedure and fluid : 



Sodium chloride ... ... ... i part. 



Magnesium sulphate ... ... 2 parts. 



Sodium sulphate ... ... ... 2 „ 



Water ... ... ... ... 100 „ 



To this mixture are added from five to ten parts of a forty per 

 cent, solution of formalin. After the specimen has become suffi- 

 ciently hardened, pour off the formalin solution, wash the specimen 

 in ninety-five per cent, alcohol, then keep it in ninety-five per cent, 

 alcohol until the blood-colour becomes restored, and finally pre- 

 serve it in a mixture of equal parts of glycerine and water. 



* Bolles Lee {Anat. Arn., xi.,. 1895, P- 253) calls attention to what he 

 considers an inaccurate use of the terms formol, formalin, and formaldehyde ; 

 also to the manner of stating the percentages used. He maintains that the 

 proper way of stating the strength of the solutions is to say "formol or formalin 

 diluted with so many volumes of water. " 



Parker and Floyd {Aiiat. Am., xi., 1896, p. 567) reply to the criticism 

 made by Bolles Lee in the above-cited article. They contend " that for the 

 s ake of consistency the same method of expression ought to be used for alcohol 

 — i.e., ninety-five volumes of alcohol and five volumes of water. These ex- 

 pressions seem to us unnecessarily cumbersome, and as they are in no way more 

 precise or less ambiguous to one familiar with the meaning of per cent, than 

 the expressions we used, we prefer them." 



