PUBLIC RECORD OFFICE
Reference :-
C.O. 885
22 PUBLIC RECORD OFFICE, LONDON
ALLY WITHOUT PERMISSION OF THE BE REPRODUCED PHOTOGRAPHIC- COPYRIGHT PHOTOGRAPH—NOT TO
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I appointed to consider the form of the annual reports on the destruction of animals in tsetse-fly areas in Africa has reported as follows
A schedule should be drawn up specifying the data required, which should include the following:-
Common name of animal, either local or general.
Scientific name (if known).
Sex.
Apparent age young, adult or old.
District, and precise locality if possible. Month of killing.
Method of killing.
Whether blood smears were obtained.
Any other information deemed of interest.
Copies of this schedule should be furnished to all who are responsible for the destruction of animals in the prescribed areas, and they should be required to fill in the data in the case of each animal killed. They should receive a supply of glass slides and instructions how to make blood smears (leaflet). When the returns are furnished by natives, naturally less information will be obtained.
Before measures are taken to act on the Secretary of State's instructions a list of species of animals within each prescribed area and an estimate of the respective numbers of each should be made as far as is practicable. This should be checked at intervals of six months. Information on the seasonal movements of animals is desirable. Blood smears, labelled with the name of the animal, the responsible person, the date and locality, should be obtained, when possible, from all animals destroyed; when the smears cannot be examined locally they should be sent to England as soon as possible.
Some standard of the numbers of tsetse flies should be recorded in each area before any hunting takes place. A rough standard might be obtained by sending ont a definite number of fly boys, supervised by Europeans, daily for a week (notes being kept of the character of the weather) and counting the flies, captured. At definite intervals, say three months, after the commencement of hunting this pro- cedure should be repeated, with the object of obtaining data as to changes in the occurrence of the fly. Any notable physical event, such as drought, floods, or exten- sive fires, just prior to the collection of the flies should be recorded.
2. I accept the recommendations of the Committee in full, and I have to request that you will follow them carefully.
3. Copies of the leaflet to which reference is made are enclosed herewith. If required, further copies can be sent to you.
4. I presume that you will be able to supply the glass slides which the Com- mittee wish to be given to persons who are responsible for the destruction of animals in the prescribed areas.
Enclosure in No. 99.
I have, &c.,
L. HARCOURT.
HOW TO MAKE BLOOD SMEARS FROM KILLED ANIMALS.
Blood smears can be made in many ways, most of which, after a little practice. give excellent results. In all methods it is important that only the top of the drop of blood, and not the surrounding structures, should be touched by the glass slide or cover-glass. Neglect of this precaution will result in the admixture of other fluids or débris with the smear. It matters not whence the blood is taken, but it must be free from mixture. It is best to take it from the heart or large blood vessels.
Method (1).In this method a drop of blood is taken on the surface of a slide near one end. The (ground) edge of another slide is brought into contact with this drop, which then spreads out so as to fill the angle between the two slides along the whole extent of the line of contact. On pushing the upper slide towards the other end of the lower slide a film of blood will be left behind. The thickness of this film is easily regulated, as, if the angle between the two slides is acute the film left behind will be very thin; if the angle be nearly a right angle a thick film will be left. An angle of 45° or a little more gives the desired thickness.
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A slight modification of the method is to take up the drop of blood on the edge of the upper slide and bring the drop of blood and the edge of this slide into contact with the upper surface of the lower slide and proceed as above (fig).
Method (2).-A drop of blood is taken on a slide rather nearer one end than the Another slide, a glass other, and the larger the drop the farther from the middle. rod, or, perhaps best, the shaft of a needle, is then applied to this drop so that the blood spreads along the whole of the line of contact. The upper slide, glass rod, or needle is then drawn across the lower slide, and an excellent film will be left (fig.).*
As soon as the smears dry, which they readily do, they may be wrapped in tissue or toilet paper, and put in a dry place. They should be labelled as soon as possible, preferably on adhesive (e.g., stamp) paper attached to the slide itself, or failing this, the data may be written on the paper in which the slide is wrapped. The animal's If the labels are not name, date, locality, and observer's name should be recorded. placed on the slides themselves each slide must be wrapped up separately, unless inore than one smear come from the same animal, in which case the smears may have additional protection by being placed face to face.
As blood smears deteriorate quickly in the tropics, they should be sent without loss of time to the Principal Medical Officer, who will arrange for their examination or forward them to England. They should be packed tightly in a cigarette box, or If there are several, it is well to tie them in such a way that they do not get broken. firmly together.
Adapted from Daniels (C. W.) & Newham (H. B.). Laboratory Studies in Tropical Medicine, 1911. Third Edition. London: John Bale, Sons, & Danielsson, Ltd. Acknowledginent is due to Messrs. John Bale, Sons, & Danielsson for permission to reproduce the figures.
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