792 MR EDWARD J. BLES ON THE 
quantity of this mixture can be made as a stock solution, as it keeps indefinitely. Just 
before use add 7 c.c. of formalin (40 per cent. formaldehyde solution) to each 93 c.c. of: 
the above stock solution. This killing and preserving fluid contains :— 
90 vols. 70 per cent. alcohol, 
3 ,, glacial acetic acid, and 
7 ,, formalin, in every 
100 vols. 
The fluid cannot be used with confidence when more than a fortnight old for killing, 
but embryos and larvee of Anura, if killed in a large quantity of the fresh fluid, may be 
left in it indefinitely for preservation. The same reason can be given for both these 
statements, viz. that the fluid after a fortnight has begun to decompose, which impairs 
its killmg and hardening powers but not its preserving property. The formalin and 
acetic acid both disappear from the fluid sooner or later, as can easily be proved by the 
disappearance of their characteristic odours; these are replaced by an aromatic odour 
mixed with that of the spirit, and this mixture is as good a preservative as pure 70 per 
cent. alcohol. This property of purifying itself, as it were, makes the fluid particularly 
useful for recommending to collectors at a distance. Specimens can be killed in it and 
then either sent off in the same fluid or forwarded in a change of the fluid after twenty- 
four hours, according to the bulk of the specimen and the relative size of the bottle or 
jar. It will then travel any distance without further preparation. 
From the reports of friends and colleagues who have used this mixture and from 
my own experiments, I gather that it is useful for the most diversified objects, from the 
egos and yolky larvee of Echinoderms to the larvee and adults of Anopheles, the newly 
hatched fry of Salmo fario, and a full-grown Ammocete. It is, judging from these 
examples, worth a trial on almost any object, especially yolky embryos. Of course it 
decalcifies and is useful for preserving and decalcifying small Craniates or their heads 
when required for sections. The specimens should be transferred from this fluid to 
50 per cent. alcohol, washed and passed into 70 per cent., and can then be treated as 
required. 
A Simple Prism Reflector.—All students of Anuran tadpoles have sooner or later 
felt the want of a convenient method of examining these objects from all points of view 
without the risk of damaging the specimen. A simple and cheap means of carrying 
this out is to build a trough as shown in Text fig. 1. The base is an ordinary 
3 inches by 1 inch or 3 inches by 13 inch glass slide. The sides of the trough are of 
plate glass ; the right-hand end is a piece of ordinary thin glass ; the end over the middle 
of the slide is a piece of No. 2 or No. 3 cover-glass. 
The cementing can be done in a few minutes if marine glue is used; the objects 
can then only be examined in water or formalin, but if the trough is to contain spirit 
the cement used must be carefully applied and allowed to thoroughly harden before use. 
Bichromated gelatine, Lovett’s cement, or some such spirit-proof cement can be used. 
