750 A MANUAL OF VETERINARY PHYSIOLOGY 



supply of common salt for animals. It is popularly believed that the 

 herbivora have a craving for salt, and in a wild state proceed to cer- 

 tain ' salt-licks ' periodically to obtain a supply. Bunge explains this 

 by showing that vegetable food is particularly rich in potassium, 

 and especially poor in sodium, and that the effect of potassium salts 

 is to withdraw those of sodium from the system, through the 

 potassium combining with the chlorine and being removed by the 

 kidneys. He points out that man takes common salt as an addition 

 to his diet, to meet the loss caused by eating vegetable food, but 

 makes no attempt to supplement the supply of other salts ; further, 

 that carnivora avoid salted food, as sufficient sodium chloride exists 

 in flesh. Notwithstanding Bunge's authority, it is quite certain 

 that horses may be kept in perfect health without any addition of 

 sodium chloride to their food, and what applies to them probably 

 applies to other herbivora. 



Sodium salts in the blood are essential to its proper osmotic 

 pressure, but both sodium and potassium are antagonistic to calcium 

 by promoting relaxation instead of contraction of the heart wall. 

 Speaking generally, the sodium salts are found in the fluids of the 

 body, those of potassium in the solids, though it will not be forgotten 

 that in this respect the sweat of the horse is an exception, being 

 rich in potassium salts. 



The remarkable part played by calcium in the matter of blood 

 and milk clotting has already been referred to, also the influence of 

 a saline solution in maintaining the rhythmical contraction of the 

 heart. The oxygen-carrier of the body would not be an oxygen- 

 carrier but for its iron, which renders the production of haemoglobin 

 possible. In the absence of salts the secretions would be useless, 

 and those containing globulins would precipitate, as it is the salts 

 which keep these in solution. In the case of young growing animals, 

 the skeletal structure would fail through loss of calcium and phos- 

 phoric acid — in fact, there is no tissue of the body which would not 

 be more or less affected by a shortage or entire absence of salts. 



Bunge supposes the salts of calcium enter the body in an organic 

 compound, but that those of sodium, potassium, and magnesium 

 enter and leave the body as inorganic salts. Attention is now 

 being directed to the calcium content of blood as a clinical factor, 

 its excess or deficiency being believed to play an important part, 

 particularly in disorders of the circulatory apparatus. It was 

 Ringer who, years ago, urged the importance of calcium in connec- 

 tion with the" circulation, and we have seen (p. 49), as the result 

 of his work, that it is now known the mammalian heart may be kept 

 beating for hours on removal from the body, if fed with Ringer's 

 solution and liberally supplied with oxygen. The relative part which 

 each of the salts of calcium, sodium, and potassium are believed to 

 play in this phenomenon has already been noticed. Calcium is 

 especially necessary to the contraction of the heart, which can be 

 shown to cease beating on decalcifying the blood, and its contrac- 

 tion restored on adding calcium in proper proportion, for an excess 

 has the opposite effect and stops the heart. Lime exists largely 

 in clover and hay, but only in small quantities in the cereal grains. 

 It is principally in the hay that the amount excreted by horses 

 through the kidneys is supplied. In the urine it passes from the 

 body in such quantities that it cannot be held in solution by the 

 alkaline fluid, and the urine of the horse is therefore always turbid. 

 In the body calcium exists in the form of phosphate, sulphate, and 



