The principal ill effects produced by an excess of food may be classed according to the composition of the offending article of fodder, as follows :

1. Too High A Percentage Of Water, as in the case of an unduly large consumption of rank grass or roots, gives rise to a laxative state of the bowels, which does not allow sufficient time for digestion and absorption to be carried on efficiently, and weakens the system by throwing an excessive amount of work on the alimentary canal in passing the food onwards. We have seen that it diminishes the power of breathing by increasing the volume of the stomach and intestines, and in extreme cases, as we find when horses are fed on boiled turnips, the distension produced by an easily swallowed and very bulky food, sets up serious digestive disturbances, among which we may number colic brought on by impairment of the strength of the muscular coat of the stomach and intestines.

2. An Excess Of Fibre, like that of water, injuriously increases the weight of the contents of the stomach and intestines (p. 98); and also has a constipating effect, as we may see when an animal is fed almost exclusively on straw.

3. An Excess Of Starch And Fat tends to produce an obese condition in horses which are not sufficiently worked. When the labour is severe, there is no danger of a horse eating too much food of this kind. Obesity in idle horses is apt to set up fatty infiltration of the tissues and conseqent weakening of the system, and possibly fatty degeneration. Linseed is the only ordinary horse food which contains a proportion of fat high enough to render it a laxative, if given in large quantities.

4. The Bad Results Of An Excess Of Nitrogenous Matter, although less hurtful to a busy horse than to an idle one, cannot be entirely counteracted by work, however severe or prolonged the labour may be. Its so-called "heating" effects appear to be chiefly due to (1) the presence in the system of an abnormally large quantity of waste nitrogenous products which produce a poisonous action on the body; and (2) the presence of an excess of sulphuric acid, which is formed, as Bunge tells us, from the sulphur contained in the nitrogenous debris and which is capable of acting in a destructive manner on the tissues. If the system contains a good supply of soda, potash, and lime, the sulphuric acid will become neutralised on uniting with these bases, which are found far more plentifully in hay, clover, lucerne, and bran, than in corn. Common salt is not capable of neutralising sulphuric acid, and consequently an addition of it to the food will not prevent corn from having a "heating" influence.

In the equine disease which is known to stablemen as "weed" or "Monday morning disease" (lymphangitis), we have an admirable instance of the hurtful effects of too much nitrogenous food, combined with too little exercise; for the malady in question is practically confined to highly fed horses which are put to work after having been kept for some time in a state of idleness, during which period their systems become overloaded with nitrogen. Strong work given to them while they are in this state, has the effect of causing the formation, by chemical decomposition, of an amount of poisonous products which the excretory organs cannot always remove with sufficient quickness to avoid disturbance of health. It is a suggestive fact that lymphangitis sometimes appears in horses that are in a starving condition. We have seen (p. 93) that when animals are in this state, there is a rapid breaking up of nitrogenous tissue, after the supply of fat in the system has become exhausted.

In considering the treatment for a heated condition of the system brought on by an excess of nitrogenous food, we should evidently seek for an agent which will neutralise sulphuric acid and promptly remove it from the body. Although we cannot definitely lay a portion of the blame on the presence of an excess of uric acid in the blood, the experience of human medicine tells us that when illness is accompanied by a large percentage of this acid, great relief is generally obtained by medicines which, like salicylate of soda, form soluble compounds with uric acid. If it is not convenient to use salicylate of soda, we have a cheap and fairly good substitute in bicarbonate of soda, which also acts well in helping to eliminate from the body the excess of potash obtained from the food.

The good influence of work in counteracting the evil effects of an excess of nutritious food, appears to be due chiefly to the increased supply of oxygen conveyed by the blood from the lungs to the tissues.