14 A MANUAL OF VETERINARY PHYSIOLOGY 



and gives the same reaction with nitrous acid as bile pigment — 

 viz., a play of colours. Haematoidin is, in fact, chemically identical 

 with bilirubin, and the name is now of interest merely as indicat- 

 ing the close genetic relationship of the pigments of bile to the 

 colouring matter of blood. Notwithstanding this close relation- 

 ship, it has not as yet been found possible to convert haematin 

 into bilirubin. The nearest approach to bilirubin is iron-free 

 haematin (haematoporphyrin). Again, both haematin and bili- 

 rubin may be made to yield an identical product (hydro-bili- 

 rubin) ; this product closely resembles urobilin, a pigment found 

 in the urine, and urobilin beyond all doubt is derived from bili- 

 rubin in the digestive canal, under the influence of putrefactive 

 organisms. 



White Corpuscles, or Leucocytes. — There are certain corpuscles 

 found in the blood, lymph, connective tissue, and pathological 



Fig. 6. — Amceboid Movement (Stewart). 

 A, B, C, D, Successive changes in the form of an amoeba. 



products such as pus, which possess a great family resemblance. 

 In the blood they are known as ' white corpuscles,' and it seems 

 quite certain that between the blood and the tissues a free inter- 

 change of corpuscular elements occurs ; this process is exagger- 

 ated under pathological conditions, as in the case of inflammation 

 and suppuration. 



One characteristic of these cells is their power of spontaneous 

 movement — ' amoeboid,' as it is termed. In Fig. 6 successive 

 changes in the form of an amoeba are shown, and very similar 

 changes occur in these cells. These changes in shape assist 

 materially in the passage of the corpuscle through the walls of 

 the vessels into the tissues. In consequence of their migratory 

 habits these cells are frequently referred to as wandering cells. 

 The white cells of the blood are so called in contradistinction to 

 the coloured or red cells, compared with which they exist in the 

 proportion of I to 300 to 1 to 700, depending on the source of 

 the blood. The white cells at the present time are more fre- 



