i895. FORMALIN AS A PRESERVATIVE. 419 



parts through shrinkage is avoided gives a life-like appearance as 

 satisfactory as any that can be hoped for. 



Fishes. — For these a 4 per cent, solution is ample to produce 

 the finest results. 



Amphioxus is best killed by plunging direct into the fluid. The 

 result is most beautiful ; the natural transparency is so completely 

 retained, that the internal organs can easily be traced, and the 

 buccal cirri protrude gracefully as in life, and not in the state of 

 tangled retraction seen in spirit specimens. Shrinking is quite 

 obviated, and until one can compare a formalin prepared specimen 

 with one fixed and preserved in spirit in the ordinary way, it is 

 impossible to comprehend how much shrunken the latter are. 



Elasmobranchs, such as Scylliiim, are also beautifully preserved 

 for dissection by simple immersion in a 4 per cent, solution of formalin, 

 provided the viscera, heart, and brain be freely exposed by cvitting 

 away the abdominal wall and opening the pericardium and brain 

 case. In two days the viscera attain the consistency of gutta-percha. 

 Objectionable smell is quite obviated, the muscles assume a snowy 

 whiteness, and the preparation as a whole becomes so clean and 

 sweet that it is a real pleasure to dissect it. Anyone who has 

 dissected an old-time Scyllium can understand what an improvement 

 this means. 



Recapitulation of Results. — For histological details, preser- 

 vation by simple immersion in a strong solution of formalin gives 

 fair results ; prior fixation by one of the accepted and appropriate 

 methods gives even better, but both are unmistakably inferior to those 

 produced by fixing and grading into spirit in the ordinary way. 



A minor and very useful employment of formalin in microscopical 

 technique is, I find, to add 3 per cent, to aqueous staining fluids, to 

 obviate any chance of the maceration of objects placed therein. Again, 

 it may be employed as a 3 per cent, solution, in place of pure water, 

 in the washing out of ordinary fixatives. I have known many 

 valuable preparations spoiled in the washing out, some by being 

 inadvertently left in too long, and others, again, deteriorated through 

 lack of sufficient washing, due to a fear of possible maceration. By 

 the employment of a formalin washing solution, ample time can be 

 allowed for getting rid of the fixative without the least fear of 

 maceration, as, even if the preparation be left washing longer than 

 intended, the formalin will prevent any ill effects. 



For dissecting and museum specimens, simple immersion in 

 formalin solution gives, except in the case of Ctenophora, Turbellaria, 

 Clurtopteyns and allied worms, Dalauoglossiis, and a few others, results not 

 inferior to those obtained by ordinary fixation and grading into strong 

 spirit, while in the majority of cases the results are greatly superior. 



Professor de Oliveira believed that formalin would preserve 

 natural colouring little impaired, but my prolonged experiments 

 negative this, for while the loss of colour proceeds much more slowly 



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