Eventually Howard and McCarrison met and the missing link in the Hunza chain was supplied. McCarrison embraced Howard’s work with enthusiasm. In his series of Cantor lectures delivered before the Royal Society of Arts in 1936 (published in book form under the title Nutrition and National Health) McCarrison said, “Further, the quality of vegetable foods depends on the manner of their cultivation; on the condition of soil, manure, rainfall, irrigation. Thus we found in India that foodstuffs grown on soil manured with farmyard manure were of higher nutritive quality than those grown on the same soil when manured with chemical manure. Spinach grown in a well-tended and manured kitchen-garden was richer in vitamin C than that grown in an ill-tended and inadequately manured one. Examples of this kind might be multiplied, but these suffice to indicate ways in which agricultural practice is linked with the quality of food. . . .”

In 1926, at Madras, India, McCarrison again proved that grains grown with compost as the fertilizer element contained more vitamins than those on which artificial fertilizers were employed. The Journal of Indian Medical Research (14:351, 1926) gives a full description of these tests. In the Journal of the Royal Society of Arts January 2, 1925) McCarrison said further, “Does the nutritive and vitamin value of cereals vary with the conditions of their growth? During the course of an exhaustive inquiry into the food value of the various rices in common use in India, I had reason to suspect that such might be the case. I found that various paddies varied considerably in their nutritive values. I could find no reason for this in their chemical composition. So it occurred to me that it might be due to differences in the content of vitamins, i. e., of substances which are incapable of detection by chemical means. Such differences might, I thought, be brought about by differences in soil or manure, or other conditions of growth of the grains. It was not possible to put this conception to the test in the case of rice, but it was possible to do so if I used millet, which is another staple grain largely used in India. Accordingly, Dr. Norris, Agricultural Chemist to the Madras Government, had nine of the experimental plots at the Agricultural Farm, Coimbatore, sown with the same millet seed. These plots have been in existence for 15 years or so and have been manured in different ways. One had no manure in all this time; another was manured with nitrates; another with phosphates; another with potash; others with various combinations of these, including one which received a complete chemical manure; the ninth plot has been manured with the natural manure of cattle. When the time came these various plots were cropped, the crops weighed and samples from each crop analyzed by Dr. Norris. There were the usual variations in quantity of the crops, and the usual differences in chemical composition associated with different forms of manuring, but the chemical analysis provided no consistent evidence that the nutritive value of the different samples might vary because of variations in certain chemical constituents of the grain. When I came to test the quality of these grains by feeding-experiments on animals, I found that the millet grown on soil manured with natural cattle manure was more nutritious and contained more vitamins than that grown on an exhausted soil, the latter being the worst of all in these respects. I was in the middle of this work when my researches came to an untimely end owing to financial retrenchments in India, so I was not able to repeat the experiments, nor to extend them to other grains. I wish, therefore, to be very guarded in drawing conclusions from them, but it does seem that the nutritive and vitamin values of millet seeds depend on the manurial conditions of their growth.” This observation is of tremendous significance and opens up a field of investigation which may prove to be of great importance not only for India, but for other countries.

Several other investigators, M. J. Rowlands and Barbara Wilkinson, carried out tests which gave similar results. In the Biochemical Journal (Vol. 24 No. 1, 1930) they say, “This research was undertaken because one of us (M.J.R) had noticed that pigs which were fed on home-grown and home-ground barley and wheat always did much better than those pigs which were fed on purchased barley and wheat, and that certain cattle did better on certain fields. It was decided to find out whether this was due to the lack of lime or other mineral constituents of the land. The results of this investigation were not satisfactory. It was then decided to try the effect of artificial manure versus dung.

“A crop of clover and grass was grown, one-half fertilized with dung, the other half with chemical fertilizers including basic slag, kainit and sulphate of ammonia. Then rats were tested by feeding them the product of these fields . . . .

“. . . . the rats were divided into two lots; one lot was put on a deficiency diet with 20 per cent of the ‘artificial’ seed . . . The rats on the ‘dung’ seed showed good growth or a slightly subnormal growth. . . . The rats on the ‘artificial’ seeds all grew very poorly, not one giving normal growth. . . . It can be seen that the former have gained nearly twice as much as the latter. . . . The rats on the ‘artificial’ seed were in a poor condition; in some the hair was falling.””