74 Chapter IV 



phenomena that follow extravasation of blood produced artificially in 

 the subcutaneous tissue of the pigeon, rabbit and guinea-pig. In all 

 these animals the haemorrhage is early followed by exudative inflam- 

 mation, during which the leucocytes come up in great numbers and 

 ingest the red blood corpuscles which are modified in the interior of 

 the leucocytes. There is a formation or deposition of pigment and 

 finally all traces of the red corpuscles disappear. In Mammals the 

 pigment is brown or brownish, just as it is in the Planarians and 

 in the "ver blanc^'; in the pigeon it is green and resembles that 

 found in the Actinians. In short there is a great analogy between 

 the resorption of red corpuscles and the true intracellular digestion of 

 the red blood corpuscles that goes on in the intestinal cells of the 

 Invertebrata. 



But what is the nature of these amoeboid elements that intervene 

 in the resorption of the extravasated blood ? At the period when 

 Langhans carried out his investigation, we were unable to differentiate 

 the cells at all satisfactorily. It is only since the publication of 

 Ehrlich's classic researches on the white corpuscles that we have 

 been able to bring more order into this question. Thanks to the use 

 of various aniline stains, Ehrlich was able to arrange the leucocytes 

 found in the Vertebrata into several definite groups. 



The question has already been touched upon in our eighth lecture 

 on inflammation ; it is therefore unnecessary to treat it here at length. 

 We must, however, before entering on the analysis of the essential 

 phenomena in the resorption of cells, as we now understand them, 

 give a rapid survey of the different varieties of amoeboid cells that are 

 found in the Vertebrata. 

 [80] Beside mobile amoeboid cells, represented by several forms of 

 white corpuscles, we must distinguish fixed amoeboid cells. These 

 are permanently fixed in certain situations in the body; this, however, 

 in no way prevents them from throwing out amoeboid processes in 

 various directions and seizing foreign bodies or certain elements 

 of the same organism. The nerve cells, the large cells of the splenic 

 pulp and of the lymphatic glands, certain endothelial cells, the cells 

 of the neuroglia, and perhaps some connective tissue cells, belong to 

 the category of fixed amoeboid cells. All these elements, under 

 certain conditions, are able to ingest solid bodies; consequently, they 

 act as phagocytes. With the exception of the cells of the nerve 

 centres, all these fixed phagocytes are of mesoblastic origin. It has 

 been much discussed whether certain processes of the nerve cells may 



