4 6 



THE WHITE BLOOD-CORPUSCLES. 



NUMBER OF LEUKOCYTES IN PROPORTION TO THE RED BLOOD- 

 CORPUSCLES IN SHED BLOOD. 



The movement of the leukocytes observed by Wharton Jones in 1846 

 in the ray, and by Davaine in 1850 in man which has been desig- 

 nated ameboid, because it corresponds entirely with that of the ameba, 

 is due to alternate contraction and relaxation of the protoplasm 

 surrounding the nucleus. It can be recognized especially from the 

 fact that processes are sent out from the surface and withdrawn (Fig. 7) 

 like the pseudopods of the ameba. At the same time the protoplasm 

 has an internal current, which can be seen particularly in the polymor- 

 phonuclear cells. Movement has been seen also in the nucleus itself. 

 The movement is attended with two sets of phenomena: (i) The migra- 

 tion of the cells, inasmuch as they draw themselves along by means of 

 protrusion and retraction of their viscid processes. In this way they 

 may migrate even through the interstices of intact vessels. Arnold 

 considers the capability of certain wandering cells to develop into 

 epithelioid or giant cells as demonstrated. (2) The taking up of 

 small granules, such as fat, pigment, foreign bodies, which at first adhere 

 to the surface and through the internal current are drawn into the 

 interior of the leukocytes and which filially may be again extruded, in 

 the same way as amebae take up food. Thus they take up fat-globules, 

 peptones and albuminous bodies that have gained entrance into the 

 blood-stream and which they may later deposit elsewhere. 



Metschnikoff dwells upon the activity of the leukocytes in retrogressive pro- 

 cesses, the parts to be broken down being taken up in the forms of particles and 

 therefore in a measure devoured. He designates the cells with these activities 

 as devouring cells phagocytes. Thus they act as chondroclasts and osteoclasts 

 in the absorption of cartilage and bone respectively. Cells of similar activity 

 are found in the tails of batrachia, and which take up portions of the tissue, 

 as, for instance, fragments of fibrils, in the disappearance of the tails during 

 the process of metamorphosis. (See also absorption of the deciduous teeth.) 

 Thus, schizomycetes or particles of other substances that have gained entrance 

 into the blood have been found taken up in part by leukocytes. Later, the leu- 

 kocytes yield up these substances to the endothelial cells of the capillaries of the 

 liver and the lungs, less commonly of the spleen. The motility of the leuko- 

 cytes is destroyed by quinin. 



The leukocytes exhibit still another interesting peculiarity, namely that of 

 chemotaxis (chemotropism) , which consists in the attraction of freely motile 

 cells like some lower organisms by certain substances, and their repulsion by 

 certain others. Especially the metabolic products of pathogenic and non-path- 

 ogenic microorganisms exert a strong attractive influence upon the leukocytes. 



