CH. IV] THE BLOOD AND THE ORGANS OF CIRCULATION 57 



(appearing yellow when looked at singly) are by far the most 

 nnmerons, there being aliout oOO of these to one leucocyte or 

 white corpuscle in normal human blood The erythroc3i:es in 

 nearly all mammals are minute, circular, biconcave discs. They 

 have no nuclei. They consist of protein material containing a 

 red-coloured substance called haemoglobin, which itself can be 

 resolved into a protein and an iron-containing substance termed 

 haematin. The leucocytes are generally slightly larger, but vary 



Fig 33. White corpuscles or leucocytes from blood (from Seliafer). 

 a. polymorph, 1). lymphocyte, c. macrocyte, d. eosinophil. 



in size according to the variety to which they belong ; they are 

 round or amoeboid in shape, and ma}' have one or more nuclei, 

 and they possess the power of independent movement. Some 

 of them are ]ihagocytic and can ingest bacteria or other foreign 

 bodies after the manner of an amoeba. Thej' tend to congregate 

 in any area of inflammation or disturbance, and one of their main 

 functions is undoubtedly to protect the organism against disease 

 or the results of injur3^ They have different staining reactions 

 according to kind, some having acid and some basic affinities. 



The red corpuscles are produced in bone marrow, which is 

 richly supplied with vessels. Certam kmds of white corpuscles 

 also have their origin in bone marrow, but others are formed from 

 the lymphocytes of the lymphatic glands. 



Blood which has been recently' shed also contains platelets, 

 which are circular bodies smaller than corpuscles. They have 

 been supposed to represent nuclei extracted from erythrocytes 

 in the process of their development, but it is uncertain whether 

 they are really present in nonnal unaltered blood. 



