920 PHYSIOLOGY 



of the blood. The granules are practically invisible in fresh specimens, 

 in this respect presenting a contrast with the eosinophile granules. 

 The leucocytes as a whole undergo variations in number according to 

 the physiological state of the animal and are increased during digestion, 

 specially of a protein meal. They vary from one in 300 to one in 600 

 red corpuscles, or, taken as a whole, from 18,000 to 36,000 per cubic 

 millimetre of blood. 



FORMATION OF THE LEUCOCYTES 



In classifying the white corpuscles of the blood it is essential to 

 know whether the different varieties we have described represent 

 phases in one and the same corpuscle or a number of different cells of 

 separate origin. The question as to the specificity of each kind of 

 leucocyte cannot be regarded as settled. According to some observers, 

 Gulland and others, all the leucocytes are derived from one kind of 

 cell, namely, the lymphocyte. Ehrlich and his school, on the other 

 hand, regard each type as forming a tissue sui generis, originating in 

 separate localities and from distinct kinds of cells. Since division of 

 the leucocytes in the blood itself appears to be an occurrence of the 

 utmost rarity, we must locate the original seat of formation of these 

 cells in two tissues. Lymphocytes are derived from the adenoid 

 tissue forming the lymphatic glands and the lymph nodules surround- 

 ing so many of the mucous cavities. These lymphatic nodules present 

 towards their centre a clearer zone, consisting of cells rather larger 

 than those of the periphery and known as the ' germ centre.' The 

 nuclei in these cells present a well-marked reticular arrangement, and 

 nuclear figures are often to be seen. By the division of these cells 

 lymphocytes are formed, pushing towards the periphery of the nodule, 

 where they make their way into the lymph-sinus and are carried 

 slowly by the lymph into the blood. Some of these lymphocytes may 

 possibly pass directly through the capillary wall into the blood-stream. 



The other tissue concerned in the formation of leucocytes is the 

 bone-marrow. This is the chief blood-forming tissue of the body, 

 since it is responsible also for the production of all red blood- corpuscles 

 which are formed during adult life. In the red marrow are seen a 

 number of cells known as myelocytes. These contain a single rounded 

 nucleus and a well-marked protoplasm which may be non- granular or 

 may contain granules, generally eosinophile in character, but some- 

 times basophile. It is stated that all intermediate stages are to be 

 found in the bone-marrow between these ' myelocytes ' and the 

 polymorphonuclear leucocyte as well as the eosinophile leucocyte. It 

 is certain that in the disease leukaemia, which is associated with an 

 increased number of leucocytes in the blood, there may be an increase 



