xviii.J NON-PATHOGENIC ORGANISMS. 243 



dried, stained with gentian-violet, and mounted. In such specimens 

 large cells are found, the protoplasm of which is filled with beautiful 

 small bacilli. ' When, therefore, speaking of the occurrence of bacilli 

 or other bacteria in the tissue of the lymphatic glands or other parts of 

 the wall of the bowels of a person dead of some disease or other, it is 

 necessary to bear in mind the above facts, viz., that already under 

 perfectly healthy conditions, even during life, bacteria can make their 

 way from the internal cavity into the tissue of the intestinal wall. 



Metschnikoff has pointed out (Virchow's Archiv, vol. 97, 3, p. 502) 

 that amoeboid cells in the blood and connective and lymphatic tissues 

 are capable of embodying bacteria introduced into the tissues, and he 

 called those cells phagocytes. "While there is no doubt that bacteria 

 like other granules and particles can be swallowed by amoeboid cells, it 

 is manifestly going too far to say, as Metschnikoff is inclined to do, 

 that the phagocytes play an important part in neutralizing the action of 

 pathogenic bacteria introduced into the blood and tissues by quickly 

 swallowing and destroying those bacteria. Where in a tissue pathogenic 

 bacteria find the suitable conditions for growth and multiplication, they 

 can do successful battle against the amoeboid cells, but where those 

 conditions do not obtain, the bacteria linger and die, and like other 

 particles can be swallowed up by the amoeboid cells. That the presence 

 of bacteria in the protoplasm of amoeboid cells does not indicate that 

 the former are being removed or destroyed and their action neutralized 

 by the latter, but exactly the contrary, is proved in Koch's septicaemia 

 of mice, in bovine tuberculosis, in leprosy, and in other diseases 

 detailed in former pages (see Chapter XI.). 



The assumption that where the leucocytes (phagocytes) are capable 

 and sufficiently numerous to take up and destroy the pathogenic bacteria, 

 no disease follows and immunity is the result, is contrary to some 

 elementary facts, e.g. however small the number of anthrax bacilli or 

 tubercle bacilli introduced into the blood of a susceptible animal, 

 infection sets in with certainty, while no infection follows in an animal 

 unsusceptible to the disease however large the dose of these bacilli. 

 No one would be bold enough to say that the white blood-cells differ 

 in the two animals in numbers and characters. Or to put it more 

 strongly : it would be absurd to say that in a sheep which has passed 

 through a mild form of anthrax, and as is well known has hereby become 

 unsusceptible to a second attack, the leucocytes have altered in number 

 and character, so that before the first attack they have been unable to 

 swallow up and destroy the anthrax bacilli, but by the first attack had 

 become endowed with this new power. 



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