627916-1899-Circular-Despatch-Investigation-of-Malaria — Page 2

THE HONGKONG GOVERNMENT GAZETTE, 28TH JANUARY, 1899.

Entomological forceps (two pairs), with curved ends, for holding pins.

-89

One ounce No. 20 entomological pins (D. F. Tayler and Co., New Hall Works, Birmingham. These pins are sold in boxes at 7s. 6d. per ounce, and as the pins are exceedingly fine, an ounce will go a very long way),

Common pins (three or four packets).

Gun-wad punch, No. 20 bore.

Cards (2-sheet Bristol Board) from which to punch discs; a supply of the latter should be prepared ready for use.

Needles (two or three) mounted in handles, for arranging legs and wings.

A Platyscopic Lens :-this is indispensable.

Cork-carpet or pith-one or two sheets about 6 in. square, on which to perform the operations of pinning, etc.

A strongly-made wooden box ( a cigar-box will do), in the bottom of which is fixed a layer of cork-carpet or pith (if the latter is used it should be not less than half an inch thick).

IMPORTANCE OF SENDING HOME SPECIMENS FOR DETERMINATION

IN THE BEST POSSIBLE CONDITION.

It should be borne in mind that, for the purpose of the scientific determination of species, mosquitoes cannot be collected with too great care. As important specific characters are furnished by the wings and legs, it is of the utmost consequence that these should not be denuded of their scales, or otherwise injured; unless attention is paid to this point the specimens will probably be quite worthless for determination.

SPIRIT NOT TO BE USED.

Specimens for determination must on no account be placed in spirit.

SPECIMENS TO BE PINNED IMMEDIATELY THEY ARE DEAD.

Mosquitoes should in all cases be pinned, and that as soon as possible after death; duplicate specimens for dissection can, of course, be preserved in spirit, but if this is done care must be taken, by the use of corresponding labels or numbers, to prevent confusion between species.

NUMBER OF Specimens of EACH SPECIES Required.

In collecting specimens of a species of mosquito for determination some half dozen examples of each sex should, if possible, always be obtained.

HOW TO DISTINGUISH THE SEXES.

'The harmless male mosquitoes can be distinguished from the females (which alone bite and suck blood) by the possession of plumose antenna and palpi, forming tufts in front of the head; in the females the antenna, though long, are nearly bare (having whorls of only short hair at the bases of the joints), while the palpi in the case of females of the typical genus Culex, to which the majority of the described species belong, are quite short.

METHOD OF COLLECTING AND Killing.

For capturing mosquitoes in the open an entomologist's collecting net is necessary, from which the insects can be transferred to glass-bottomed pill-boxes; in doing this great care must be taken not to pull off the legs; inside buildings it is possible, with care, to capture mosquitoes on walls an1 win. dows in the pill-boxes themselves. In any case mosquitoes should be collected alive in the glass- bottomed pill-boxes*; if care is taken, several specimens can be got into one pill-box. To kill the mosquitoes the box is opened a fraction of an inch on one side, and placed for a few minutes in a cyanide killing-jar,† which must, of course, be closed. As soon as the insects are quite dead (if the mixture in the jar is of reasonable strength from three to five minutes is sufficient, and mosquitoes should not be allowed to remain exposed to the effects of the cyanide longer than this) they should be turned out on to a sheet of cork-carpet or pith; they should be touched as little as possible, the mani- pulations necessary in arranging the wings and legs being performed with a needle,

* These boxes can be obtained from any dealer in natural history apparatus, but care should be taken to see that the bottoms-and not the tops, as is often the case--are made of glass. Since the boxes are constructed of cardboard, they are liable in tropical countries to go to pieces in the rains, and to prevent this they should be covered with glazed jaconet (stuck on with liquid glue) and then coated with Aspinall's enamel. A cyanide killing-bottle can be procured ready for use from Hinton and Co., Bedford Street, London, W.C., or any other chemist will prepare one to order, but when mosquitoes (or indeed any Diptera) are collected in the manner here advised it is preferable to make a large- sized killing-jar for oneself as follows:-Take any fairly large glass jar (such as a pickle-bottle) with a wide mouth and closely fitting lid, and cover the bottom with a layer of dry plaster of Paris to the depth of half an inch; pour in above this a layer equal in depth consisting of powdered cyanide of potassium, mixed with rather more than its bulk of dry plaster of Paris; cover this mixture with a layer of dry plaster of Paris to the depth of a quarter of an inch or so, and pour in above the whole à layer, half an inch in depth, consisting of plaster of Paris mixed with water to the consistency of cream. As soon as the top layer of plaster is dry the jar is ready for use. To obviate the risk of cracking the jar owing to the heat evolved when plaster of Paris is mixed with water, it may be advisable to stand the jar in warm water before adding the final layer. The exact amount of eyanide of potassium to be used is of no great consequence, but in the case of a properly prepared jar the odour should be readily perceptible on removing the lid; if it is not, the reason may be that the mixture is too dry, when a little water poured on to the top layer will probably set matters right. After some months' use the cyanide loses its efficacy (to obviate this so far as possible the jar should never be allowed to remain open), and the mixture must then be renewed.