iv THE BLOOD: FORMED CONSTITUENTS 115 



Notwithstanding these different theories and conflicting argu- 

 ments, Ehrlich's view is that generally supported. 



In the circulating blood the white corpuscles are almost always 

 round, and since their specific gravity is somewhat lower than 

 that of the erythrocytes, they leave the more rapid axial current 

 of the vessels and follow the slower peripheral stream, keeping in 

 perpetual contact with the internal walls of the vessels and con- 

 stantly rotating along them (cycloid movement). When observed 

 in an isolated drop of blood, the object-carrier of the microscope 

 being warmed to 35-40 C., it is easy to recognise their mobility, 

 which exactly resembles that of the Amoeba, so that Lierberktihn 

 (1854), who was the first to study and describe them exactly, 

 regarded leucocytes as peculiar parasitic amoebae. It is more 

 interesting to watch the amoeboid movements of the leucocytes 

 within the blood- stream. Cohnheim (1869) was the first to 

 demonstrate the fact that leucocytes, by their amoeboid properties, 

 are capable of perforating the internal walls of the smallest veins 

 by a pseudopodium and of passing their whole body, little by little, 

 through the temporary wound thus formed, as through a inesh, 

 emigrating in this way from the blood torrent into the interstices 

 or plasma canals of the tissues. This emigration may become 

 tumultuous in tissues that have suffered inflammatory irritation 

 (natural or experimental). The pathological doctrine of suppura- 

 tion and formation of abscesses is definitely co-ordinated with 

 this fact. The more recent researches of Thomas, Eecklinghausen 

 and others have demonstrated that corpuscular diapedesis must be 

 regarded not as a passive extravasation, but as an active emigra- 

 tion due (as was Cohnheim's original idea) to the amoeboid 

 mobility of the leucocytes. 



The discovery of Phagocytosis, founded more particularly on 

 the elegant researches of Metschnikoff (1892), added new and 

 interesting arguments for the close approximation between 

 leucocytes and amoebae. Even when removed from the blood, and 

 observed with the microscope, leucocytes, like amoebae, are seen to 

 be capable of ingesting many foreign bodies, by surrounding them 

 with protoplasm, whether these are inorganic particles (such as 

 carmine granules and other colouring matters), fat drops, dead cells 

 or fragments of cells, or living cells and microbes (e.g. erythrocytes 

 and bacteria) of various pathogenic or non-pathogenic species. 



Leucocytes, like amoebae, are capable of digesting dead bodies, 

 and of chemically killing and dissolving the living cells and 

 microbes which they have ingested. The red corpuscles thus 

 dissolve slowly in the interior of the phagocytes (large leucocytes), 

 leaving a residue of pigment. They exercise a similar dissolving 

 action upon pus granules (dead or dying leucocytes), on the fibrin 

 of inflammatory exudates, and on muscle fibres in cases of acute 

 atrophy of the muscular tissue. Lastly, the phenomenon of the 



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