224 MANUAL OF PHYSIOLOGY. 



It is then not unreasonable to suppose that many of the white 

 cells found in the blood have their origin in these organs. 



They may also be developed from similar cells in any tissue, 

 but their multiplication by division, other than that which prob- 

 ably occurs in the lymph follicles where it cannot be seen, is a 

 circumstance of the greatest rarity, and few observers have been 

 fortunate enough to witness the phenomenon. 



The destiny of the white blood-cells is probably manifold. 

 From the readiness with which they escape from the capillaries 

 and wander by their amoeboid movement through the neighboring 

 tissues to reach any point of injury, it would appear that they 

 take an active part in the repair of any tissue whose vitality has 

 in any way suffered. During the growth of all tissues the cells 

 seem to contribute active agents in their formation ; thus in the 

 formation of bone it has been stated that escaped blood-cells or 

 their immediate offspring help to lay down the calcareous mate- 

 rial, and some even settle themselves as permanent inhabitants 

 of the lacuna}. 



Further, they are in all probability the means of renewing the 

 red disks. Their protoplasm either takes up the coloring matter 

 from its surroundings, or forms it within itself from suitable ingre- 

 dients. Certain it is that cells are found which are recognizable 

 as white blood-cells which have more or less of the red coloring 

 matter imbedded in their substance. As this increases the cell 

 gradually loses its distinctive characters and assumes those of a 

 red corpuscle. Such elements, it will be seen, are common in the 

 spleen and the blood leading from it. 



THE RED CORPUSCLES. 



The red disks were discovered in the human blood by Leuwen- 

 hoek, about 1673. They alone give the red color which charac- 

 terizes the blood of all verteb rated animals (except the am phi- 

 ox us), but are not found in the blood of the invertebrata, which 

 only contains colorless cells. When the blood of the inverte- 

 brates has a color, it owes it to the fluid, not to the corpuscles. 

 The individual disks when viewed singly under the microscope 



