78 Chapter IV 



the dasmatocytes of Ranvier, never ingested foreign bodies. But, 

 (especially after the researches of MesniP), we have been compelled 

 to change our opinion on this point. The true eosinophile cells are 

 able to devour foreign bodies, especially micro-organisms, and must 

 therefore be regarded as phagocytes belonging to the group of 

 microphages. 



It is the peculiar merit of Ehrlich and of his school that they have 

 thoroughly established the fact that, in Mammals at any rate, the two 

 principal groups of white cells are distinguished, amongst other 

 characters, by the diversity of their origin. The lymphocytes and the 

 mononuclear cells are developed in the spleen and lymphatic glands, 

 whilst the " polynuclear ^' cells arise from the granular mononucleated 

 myelocytes of the bone marrow. This is now generally accepted as 

 [84] applicable in the great majority of cases. In Ammocoetes, however, 

 the two chief varieties of leucocytes arise from one and the same 

 organ, regarded by several observers as a kind of primitive spleen, 

 which runs along and in part surrounds the intestine. Mesnil has 

 been good enough to make sections of this primitive organ in which 

 it may be demonstrated that the macrophages and the microphages 

 in the larva of the lamprey have the same seat of origin. Frog 

 tadpoles and Cartilaginous Fishes also possess microphages which do 

 not arise from the bone marrow, since in them this tissue is completely 

 absent. But even in Mammals, at least in certain pathological con- 

 ditions, Dominici^, in a research executed with much care and a 

 perfect technique, has demonstrated the myelogenous transformation 

 going on in the spleen. Thus in the adult rabbit affected with 

 septicaemia by the typhoid bacillus, he found in the spleen de- 

 velopmental centres of amoeboid elements which, normally, appear 

 to develop in the bone marrow only, i.e. the megacaryocytes, or large 

 cells with budding nuclei, the neutrophile myelocytes (amphophiles), 

 basophiles and eosinophiles. 



The mesoblastic phagocytes of the Vertebrata are divided, then, 

 into fixed phagocytes — the macrophages of the spleen, endothelia, 

 connective tissue, neuroglia, and muscle fibres— and free phagocytes. 

 These latter are sometimes haemo- or lympho-macrophages, sometimes 

 microphages. The fixed macrophages and the free macrophages re- 

 semble one another so greatly that it is very often extremely difficult, 

 if not impossible, to differentiate them. For this reason it is often 



^ Ann. de VImt. Pasteur, Paris, 1895, t. ix, p. 301. 

 2 Arch, de med. exper., Paris, 1901, t. xiii, p. 1. 



