Volume 49 1940 > Volume 49, No. 193 > Note on a salt substitute used by one of the inland tribes of New Guinea, by J. Dickie and D. S. Malcolm, p 144-147
NOTE ON A SALT SUBSTITUTE USED BY ONE OF THE INLAND TRIBES OF NEW GUINEA
ABOUT three years ago in a letter to Dr. H. D. Skinner, Curator of the Otago Museum, Dr. Reo Fortune described the use of a substitute for common salt by a tribe living 200 miles from the sea at the head waters of the Purari River, New Guinea.
It is well known that primitive tribes whose diet is largely vegetarian have a much stronger craving for salt than tribes whose diet consists principally of meat. Such vegetarian tribes are often found to have developed the use of salt substitutes.
This note records the results of the analysis and of some feeding experiments made by us on a sample of the preparation supplied by Dr. Fortune. So far as could be ascertained from the natives the salt substitute is prepared from the ash left after burning a grass known locally as kurnai, or, in Malay, lalang. In order to identify this grass more correctly we consulted Mr. W. D. Francis, Botanist to the Department of Agriculture, Brisbane, who kindly informed us that it is almost certainly Imperata cylindrica, var. Koenigii—a grass of poor nutritive value common in the grasslands of New Guinea. Probably other materials are also used for Dr. Fortune refers to “wood ash” as well as “grass ash.” Even in small amounts ordinary vegetable ash, being distinctly alkaline, is both disagreeable to the taste and injurious to the body. The salt substitute collected by Dr. Fortune is neutral in reaction, and, as shown by our experiments, rats can consume it with no bad effects. It is remarkable that these primitive people should have hit upon a method of treating the ashes, and it would be interesting to know whether the procedure is the same as that used by certain negro tribes in Africa. We think that, after sieving away the debris, the ash is probably dissolved in water and - 145 allowed to evaporate till crystallization occurs—the alkaline mother liquor would then be rejected.
As we received it, the material consisted of several lumps of what looked like salt mixed with earthy matter. It contained 7.9 per cent. of water. On dissolving and filtering a clear solution resulted—the insoluble material left on the filter paper containing sand, amounting to 7.2 per cent. of the whole. The reaction of the clear solution was neutral, and had a bitter taste.
On analysis it gave: Potassium, 39.1 per cent., Sodium, 1.5 per cent., Calcium, 1.2 per cent., Chlorine, 19.4 per cent., Sulphate, 25.4 per cent., Phosphate, traces. These elements may be regarded as combined thus: Potas. chloride, 35.9 per cent., Sodium chloride, 3.8 per cent., Potas. suphate, 45.3 per cent., Calcium Phosphate, 4.0 per cent. It gave little or no reaction to tests for carbonates, iron, or iodine.
From these figures it is evident that the material contains a small amount of common salt, 3.8 per cent., along with relatively large amounts of potassium chloride and sulphate, and this latter feature of the analysis was of special interest to us from the physiological point of view because of the well-known work of Bunge (1).
From a study of the consumption of salt by tribes and peoples living under all sorts of conditions, as well as from personal experiments, he arrived at the conclusion that the greater craving for salt of vegetable-eaters as compared with meat-eaters is due, not only to the paucity of sodium in vegetable food, but also to the preponderance of potassium over sodium in such food. According to his observations the excess of potassium causes a loss of sodium from the body. This is true for a short experiment; but later experiments, of longer duration by later workers (2) show that the body retains its sodium in spite of a large intake of potassium. These experiments were carried out with artifically-made mixtures of the salts, and, since we are dealing here with a product used by man under natural conditions, we undertook some experiments on rats to see whether the salt substitute was capable of supplying the need of the animals for sodium salts in spite of its large preponderance of potassium salts.
The advantage of the rat as an experimental animal is that, like man, it is omnivorous, and, owing to its size, - 146 requires only a small amount of the material to be tested. Moreover, the young rat grows rapidly, and when its weight is plotted against time the resulting growth curve shows clearly any deficiency in the diet. Also, since its life span is only 3 years as compared to 60 to 70 for man, a month in the rat's life corresponds to nearly two years in man.
Seven young rats—all of one litter—were used—three bucks and four does. They were kept in separate cages and fed on a mixture of casein, fat, starch, a little cane-sugar, minerals, and vitamins. Four of them, two bucks and two does, formed the “experimental” group, while three, a buck and two does, formed the “control” group. The only difference in the food of the two groups was in the minerals given. The experimental group received the salt substitute plus a certain amount of calcium carbonate to act as a source of alkali; the amount of salt substitute used was 3.3 per cent. of the diet, a proportion which we reckoned would correspond to that used by the natives. The control group received a salt mixture (McCollum's) containing adequate amounts of all the minerals required for good nutrition. The rats were weighed every second day and a growth curve made for each; the amount of food eaten daily by each rat was also weighed.
The feeding experiment lasted for 46 days—during 27 days of that period the experimental group received the New Guinea salt in their food—this was preceded by a 9-day period on the control diet, and was followed by 10 days on the same—the change from one diet to the other appeared to make no difference to the rats, the one was as readily eaten as the other. The other group of rats received the control diet for the whole time.
At the end of the experiment a post mortem examination was made on one buck from each group.
When the two groups are compared as to (a) their growth curves; (b) the amount of fod eaten daily; (c) the gain in weight per gramme of food eaten; (d) the general appearance, coat, liveliness, etc.; (e) the post mortem appearances—only slight and insignificant differences were found.- 147
We conclude therefore that the “salt substitute,” if used in suitable quantity contains enough sodium chloride for the needs of animal life, and that it does so in spite of the large amount of potassium salts present. The material is not a substitute for common salt, for, strictly speaking, sodium chloride is a necessary ingredient of the diet of all higher animals and cannot be replaced by any other substance.
It should also be mentioned that kurnai does not appear to be a grass specially rich in sodium chloride, e.g., New Zealand lucerne yields an ash with a much higher percentage (3). The relative abundance of the grass in the district probably explains why it is used.
Dr. Fortune states that “the old men of this tribe have a curious habit of cutting themselves inside the nose to cause bleeding. The blood is caught in dishes of spinach which are then passed round to be eaten. The salt substitute is always spat with chewed ginger on to food to season it.”
When an animal is killed they carefully preserve and use the blood. As noted by Bunge this custom is common among people living largely on vegetarian diet and is due no doubt to the fact that blood contains much sodium chloride.
We wish to express our thanks for the help given us in this work by Dr. Fortune, Dr. Skinner and Mr. Francis, and to Professor J. Malcolm for help in the preparation of this note.
We are also much indebted to Dr. W. D. Hambly (4) for much interesting matter on the use of salt among African tribes which we gave more fully in the thesis of which this note is an abstract.REFERENCES
1. G. von Bunge. Textbook of Physiological and Pathological Chemistry (English trans.) (1902) p. 93.
2. H. G. Miller. J. Biological Chemistry, vol. 55, pp. 45 and 61 (1923).
3. B. W. Doak. N.Z.J. of Sc. and Tech., vol. 11, (1929) p. 108.
4. Wilfrid D. Hambly. Source Book for African Anthropology.