220 VETERINARY PHYSIOLOGY 



are partly excreted by the kidneys and are partly split up to 

 form the hydrochloric acid required for stomach digestion. 

 The phosphates and sulphates are excreted in the urine, but 

 whether they are also used in the tissues is not known. 



The leucocytes break down in the body but when and how 

 we do not know. We shall afterwards find that they are 

 greatly increased in number after a meal of proteins, and, since 

 the increase is transitory, lasting only for a few hours, they are 

 probably rapidly broken down, possibly to feed the tissues. It 

 would thus seem that a leucocyte may live for only a short 

 time in the blood. 



The erythroeytes also break down. How long they live is 

 not known. It is found, after injecting blood, that the original 

 number of corpuscles is not reached for about a fortnight, and 

 hence it has been concluded that the corpuscles live for that 

 period. The experiment, however, is far from conclusive, and 

 must be accepted with reservation. 



Organs connected with Haemolysis. The process of breaking 

 down of old erythroeytes and eliminating their pigment is 

 often called the process of haemolysis. Certain organs appear 

 to be specially connected with it, but the precise part 

 played by each of them is not very clearly understood. 



That the liver acts in this way is indicated, first, by the 

 fact that the blood passing from the organ during digestion 

 contains fewer erythroeytes than the blood going to it; 

 second, by the formation in the liver cells of bile pigments, 

 which are derivatives of haemoglobin ; third, by the presence of 

 pigment and of iron in simple combinations in the liver cells 

 under certain conditions. It is possible that the reabsorbed 

 salts of the bile acids in the portal blood dissolve the pigment 

 out of the old erythroeytes, and that the liver cells may then 

 act upon the liberated pigment. Under ordinary conditions 

 the liver does not store much iron. 



The spleen is generally said to have a similar action. This 

 organ is composed of a fibrous capsule containing non-striped 

 muscle and a sponge-work of fibrous and muscular trabeculae, 

 in the interstices of which is the spleen pulp. The branches 

 of the splenic artery run in the trabeculse, and twigs pass 

 out from these trabeculae, and are covered with masses of 

 lymph tissue forming the Malpighian corpuscles. Beyond 



