ANIMAL EXPERIMENTATION AND PROTEAL THERAPY 285 



amoeboid movement and that of ingesting foreign particles which 

 may be presented to them. On account of this power of eating 

 up foreign particles they are frequently spoken of as 'phagocytes,' 

 in this respect resembling unicellular organisms and the undif- 

 ferentiated cells of many kinds of tissue. All the phenomena con- 

 nected with the process of inflammation in higher animals are 

 directed to the assemblage of leucocytes at the spot which is the 

 seat of injury or of infection, so that they may devour and remove 

 either the injured tissue or the invading micro-organisms. This 

 process plays therefore an important part in determining the im- 

 munity of any animal against infection; though in the higher 

 animals it is assisted by a number of other mechanisms directed 

 towards the same e"nd, which we shall have to discuss in a subse- 

 quent chapter. The use of phagocytosis is not, however, confined 

 to the protection of the organism against infection. Wherever 

 any effete or dead tissue has to be cleared away, whether as the 

 result of injury or in the course of metamorphosis of organs, the 

 leucocytes play an important part. Thus in the great rearrange- 

 ment of tissues which occurs in the larval state of insects, the re- 

 moval of the muscle fibres which are no longer required is effected 

 by the accumulation of phagocytes around them. The phago- 

 cytes may send processes into the muscle substance, which dis- 

 solve this tissue and then take it up. The absorption of the tail 

 of the tadpole is effected in the same way by means of phagocytes. 

 In mammals, including man, the moulding of the long bone which 

 occurs in the process of growth is effected by continual and coin- 

 cident processes of absorption and new formation of bone. The 

 absorption is carried out by means of spinal phagocytes formed by 

 the aggregation of a number of leucocytes, the well-known 'giant 

 cells' or myeloplaxes which form so prominent a constituent of 

 bone-marrow. 



"The blood-corpuscles represent the wandering phagocytes of 

 the body. There are fixed phagocytes of which the myeloplaxes 

 just mentioned may be regarded as a type. Other members of 

 this class are the endothelial cells (Kupfer's 'Sternzellen') which 

 line the capillaries of the liver. If a suspension of carmine or of 

 micro-organisms be injected into the blood stream these endo- 

 thelial cells are found a little later to have taken up large numbers 

 of the foreign bodies. Under normal circumstances these cells 

 as well as some similar cells in the spleen take up effete red blood- 

 corpuscles and destroy them. During the process of ^degeneration 

 of a peripheral nerve brought about by its separation from the 

 ganglion-cells of which its fibres are the processes, a marked pro- 

 liferation of the nerve-nuclei takes place. These become sur- 

 rounded with protoplasm and act the part of phagocytes, loading 

 themselves with the fat globules set free by the degeneration of 

 the myelin sheath. To the same class of fixed phagocytes may 

 possibly be ascribed certain of the plasma-cells of the connective 

 tissues. 



"That the polymorphonuclear leucocytes are endowed with 

 these phagocytic properties is universally acknowledged, but some 



