The amount of soda in soil varies greatly, and consequently the percentage of soda in plants and also in the animal body is of too variable a nature to permit of our making exact calculations for determining the amount of salt which should be added to a horse's food, so as to adjust the proportion which the soda should bear to the potash. We may, however, base an approximate calculation on their proportion in milk, namely, about 2 1/2 parts of potash to I part of soda. Take, for instance, the case of meadow hay, which, according to Warington (Chemistry of the Farm), contains 28.8 oz. of potash and 5.21 oz. of soda in every 100 lb. Here the proper amount of soda, taking milk as a standard, should be 11.52 oz.; the deficiency being consequently 6.31 oz., which is made up of 4.68 oz. of sodium and 1.63 oz. of oxygen. To supply the missing 4.68 oz. of sodium by means of common salt (sodium chloride), we shall require 11.9 oz. (say 12 oz.) of that mineral. Supposing, therefore, that we give a horse an inclusive daily ration of 30 lb. of meadow hay, we ought to add to it about 3 1/2 oz. of common salt; or at least 1 oz. for every 10 lb. of meadow hay. Church (Food Grains of India) tells us that "the due admixture of food-grains belonging to different classes will secure the necessary mineral ingredients, provided an allowance of at least 230 grains of common salt be added to the daily ration of a man having a body weight of 105 lb." This would be equivalent to about 5 oz. for a horse weighing 1,000 lb. Church also states that "the amount of salt consumed per head per day in the Bombay Presidency just exceeds 1/2 oz.; in Sind it is calculated to be a little more than 1/4 oz." I draw attention to these Indian statistics, because salt being an excisable article in India, the amount of its consumption can be obtained with a fair degree of accuracy, and as the vast majority of the inhabitants of that country are very poor, they are forced to practise rigid and often unhealthy economy in its use. These comparative considerations will, I think, support my contention that a horse fed exclusively on hay or grass should have a daily supply of not less than 3 1/2 oz. of common salt. Continuing this line of calculation, we are enabled to construct the following approximate table: -

Lime is required chiefly for the building up of bones, which process is active in young animals, but is slow in adults, because bone is a comparatively stable tissue. Lime is far more easily absorbed from vegetable food than when given as a mineral addition to the food, as for example, in the form of lime-water or chalk. Hence, if the soil that produces grass which is given to young horses is poor in lime, it is well to make up the deficiency through the grass by manuring the ground with bone manure or lime. Soluble phosphate of lime is the form in which an artificial supply of lime is most easily taken up by the system.

As maize is poor in lime and other mineral matters, it is not a suitable food for young horses; although it answers fairly well for adult horses. Oats are much richer in lime than maize, barley, or wheat. Hay, and particularly lucerne hay and clover hay, contain a large percentage of lime.

Deficiency in the mineral matter of food is not an unfrequent cause of ill-health or at least want of vigour in horses, which in such a case will evince their craving for the substances of which they are in need, by licking the plaster off walls, eating dirt, and preferring muddy water to clean water to drink.

We learn from the experiments made by Henry on growing pigs, that an addition of bone meal to the food greatly increases the strength of the bones. A similar result, though to a lesser extent, was arrived at by an addition of wood ashes. These experiments lasted from 84 to 128 days. In 112 days, two pigs consumed 10 1/2 lb. of bone meal and 7 1/2 lb. of salt; and in the same time, two other pigs consumed 33 lb. of hard wood ashes and 8 lb. of salt.

Attention may with advantage be directed to the fact to which I have tried to give prominence in the foregoing pages, that the quality of the muscles, tendons, ligaments, bones, fat, and other tissues greatly varies according to the food upon which an animal is fed. Although we all know that this is the case in butcher's meat, some are inclined to think that for working purposes "bone is bone" and "muscle is muscle," whatever has been the food upon which they have been produced.