onchocerciasis. In both cases the microfilariae were mounted under cover-slips in normal saline on slides and immobilized from below by the heat of a naked flame. Microfilariae of 0. ocher@ were distinguished from those of 0. gutturosu or 0. armillat~, species which also occur in cattle in the area, according to the characters described by BAIN et al. (1977). 0. dukei has not been recorded in Mali. Each microtilaria was drawn using a camera lucida at 10x magnification. The lengths of the microfilariae were obtained from the drawings using a pair of dividers with a fixed interval, equivalent to-20 u long.

The lengths of 267 microfilariae of 0. ochengi ranged from 260 to 338 u with a mean of 289.12 (S.E. = 1.01). 355 microfilariae of 0. voZvulus ranged in length from 256 to 330 u lona with a mean of 284.9?(S.E. = 0.78). These means are significantly different (d = 3.25; KO.002). However, because of the wide range of sizes found and the extent of the overlap in sizes it is not possible to use simple measurements of length to separate the microfilariae of the two species. This is also true for the infective stages of the two species, reared in and dissected from adult Simulium damnosum s.1. (A. M. Denke, unpub- lished observations). OMAR & GARMS (198 1) reported that some unidentified Onchocerca larvae found in S. damnosum sl., which were enzymatically separable from those of 0. voZvulus but morphologically very similar were significantly longer: but Omar and Garms also concluded that this finding was of no value for distinguishing the larval types. Histochemical studies of the developing stages of known 0. ochengi and 0. volvulus have also failed to reveal reliable distinctions (OMAR et al., 1979).

The studies were conducted while I was a consul- tant for the WHO Onchocerciasis Control Programme and I am grateful to the then Director, M. Ls. Bazin, and to Dr. J. F. Walsh, Chief of the Vector Control unit at the time, for providing the opportunity for the study. I am also indebted to Dr. H. Aaoua, latelv sector Chief at Bamako, and his staff for their assistance. I also thank Dr. R. A. Cheke for translating my French manuscript and for his com- ments.

A. M. DENKE Institut National #Hygiene, Ernst Rodenwaldt, BP. 1396 Lomi, Togo

References Bain, O., Denke, A. M., Amegee, Y. & Chabaud, A. G.

(1977). Les onchocerques des bovins au Togo les microfilaires et leurs distributions. Annales de l’llniversitb du B&in, Togo, 3, 117-123.

Omar, M. S., Denke, A. M. & Raybould, J. N. (1979). The development of Onchocerca ochengi (Nematoda: Filar- ioidea) to the infective stage in Simulium dumnowm s.1. with a note on the histochemical staining of the parasite. Tropenmedizin und Parasitologic, 30, 157-162.

Omar, M. S. & Garms, R. (1981). Histochemical differentia- tion of filarial larvae found in Simulium damnosum s.1. in West Africa. Tropenmedizin und Parasitologic, 32, 259- 264.

Accepted for publication 16th May, 1985.

Origami and oral rehydration A wide variety of methods has been suggested to

measure the appropriate quantities of salt and sugar for oral rehydration. These include a two-ended spoon, a piece of wood and two holes in it, and versions made from bottle tops and local spoons.

One of us (B.Y.) who is involved with the CHILD-to-child programme and is presently writing a health education text for primary school teachers in developing countries, was concerned to find a simple way to present the idea in the classroom, to make it more “teachable”. When his 12-year-old son who had an interest in Origami was presented with the problem, he went away and returned with a paper cup. For the sugar, a piece of paper 6 cm square is needed; for the salt, an equivalent piece 3 cm square. It is made as shown in the figure.

AC

c AC

The cups need to be opened so that they will hold the maximum amount of salt and sugar. The salt and sugar should be level with the top of the cup and not heaoed. To check that the container for the drink is the-right volume, a cup made from paper 20 cm square can be used. Two of these made a suitable volume of 200 to 250 ml.

We have tried out the idea with 8 and 9-year-old Mombasa schoolchildren. They had no difficulty in making the cups and thoroughly enjoyed learning a simple yet practical and usable idea.

‘British Council BEVERLEY YOUKG’

DAVID MORLEY' ‘University of London Institute for Child Health, 30 Guilfmd St., London, W.C.I.