362 A MANUAL OF VETERINARY PHYSIOLOGY 



The table shows that in all cases the chief increase in body 

 weight is due to the deposition of fat. The ox lays on the most 

 protein, the sheep stores up the largest amount of salts, the pig 

 puts on the most fat, and fattens, not only on the smallest 

 amount of food, but in the shortest time. The table on p. 343 

 shows that in a given weight of body substance, animals passing 

 from the lean to the fat conditions lose nitrogenous and mineral 

 matter ; in oxen and sheep the fat increases nearly twice, and in 

 pigs fully twice as much as in the lean state. The water diminishes 

 and the total dry substances increase in passing from ' store ' to 

 fat condition. 



Water. — The amount of water found in the tissues of animals 

 is very constant, and* as may be seen from the table on p. 343, 

 the total body water in animals in different conditions of fatness 

 is shewn to be very similar. The muscles of creatures as far 

 removed as the pig and the snail, the ox and the lobster, contain 

 78 to 79 per cent., and other tissues are equally uniform. We 

 have just seen that in fattening animals the body loses water, 

 the tissues in consequence becoming drier (see table, p. 343). 



Under the influence of rest and work varying quantities of 

 water are lost, and in hot weather the loss is still further increased. 

 It has been calculated that a man may lose water at the rate of 

 5 per cent, of his body weight on a hot day, and that muscular 

 work in hot weather may increase the output of water as much as 

 six times ; but we are not aware of any exact experiment on this 

 question on animals, though we know practically that the loss of 

 water is considerable. Of the total water received in the food 

 or consumed, the bulk passes away by the kidneys ; during work 

 a considerable amount is lost by the skin and lungs, and less in 

 consequence passes by the kidneys. 



The very constant proportion of water in the tissues shows 

 that the consumption of excessive amounts of fluid does not lead 

 to storage. Adjustments are readily effected, and the excess of 

 fluid in the blood is rapidly got rid of. All animals withstand 

 a deficiency of water badly ; the horse is probably the weakest 

 in this direction, and shortage of water is far more immediately 

 serious for any horse than shortage of rations. A thirsting 

 animal dies when it has lost 10 per cent, of its body weight in 

 water, though 50 per cent, of its protein and the whole of its fat 

 will disappear before death from starvation ensues. A man may 

 avoid putting on weight by keeping himself short of fluid, and 

 horses will rapidly lose condition by having their water supply 

 limited. Without sufficient water neither rumination nor 

 intestinal digestion in herbivora can go on ; the contents of 

 the rumen of the ox and of the colon and caecum of the horse 

 must be kept fluid, and much of the water consumed is devoted 



