284 HELEN DEAN KING 



ought to define the hmits of the use of formalin as a brain pre- 

 servative and to indicate when and how this substance can be 

 used to the greatest advantage in neurological work. The pres- 

 ent paper records the results of such a series of experiments made 

 on brains of the albino rat (Mus norvegicus albinus). As a 4 

 per cent solution of formaldehyde (10 per cent formalin) is the 

 one that the experience of many investigators has shown is the 

 best for brain preservation as well as for general histological work, 

 a solution of this strength was the only one used in this series 

 of investigations. 



The technique employed in all the experiments was as follows: 

 Animals of known ages were killed with ether, and their body 

 lengths and body weights recorded. The brain, with its menin- 

 ges intact, was removed as soon as possible after the death of 

 the animal, being cut from the cord at the tip of the calamus 

 scriptorius. Each brain was then weighed to a tenth of a milli- 

 gram in a closed weighing bottle and placed on absorbent cotton 

 in a definite amount of 4 per cent formaldehyde. The glass 

 stoppered bottles in which the brains were kept were of uniform 

 size, and they were inclosed in black covered cases to exclude 

 light as, according to Fish ('95), this precaution will prevent the 

 decomposition of the solution and the subsequent formation of 

 paraformaldehyde. The brains were weighed at definite times 

 which varied somewhat in different series of experiments. On 

 removal from the solution the brain was placed for a moment 

 on filter paper to remove the superfluous liquid, it was then 

 weighed as quickly as possible in a closed weighing bottle and 

 returned to the solution. After a final weighing at the end of 

 a stated period, the brains were dried for one week in a water 

 bath which had a temperature of about 95°C. They were then 

 cooled in a desiccator and reweighed in order to determine the 

 effects of the solution on the percentage of solids in the brains. 

 In some few cases, after the final weighing, brains were trans- 

 ferred into alcohol, imbedded by the celloidin-paraffine method 

 of Bodecker ('08), and then sectioned and stained with thionin 

 in order to ascertain the histological effects that had been pro- 

 duced. 



