Phagocytosis

(fag-o-si-to' 'sis). The destruction or taking up of microorganisms or other solid elements by living cells, as by colorle blood-corpuscles. This theory has been advanced by Metschnikoff and others to explain immunity. It has been found that if microorganisms, such as anthrax bacilli, are introduced into an insusceptible animal, some of them will be found within the bodies of leukocytes, while this does not occur in a susceptible animal. This fact has led to the enunciation of the doctrine that immunity or susceptibility depends on the ability or inability, respectively, of the body-cells to destroy microorganisms. Immunity may be congenital or acquired; in the latter case it is brought about by an adaptation of the cells to the end that they can consume virulent organisms without harm. Several arguments have been advanced against Metschnikoff 's views. It has been said that the bacteria sometimes found in leukocytes are probably dead; if a living microorganism enters a colorle blood-corpuscle, the latter is more likely to suffer than the former. Again, the symptoms of infectious diseases are due to pecidiar poisons rather than to the bacteria as such. Immunity can be conferred upon an animal by injections of appropriate doses of such poisons, a fact that cannot readily be explained by the phagocytic theory. It has also been demonstrated that the blood-serum po e es bactericidal properties, and that the blood-serum of artificially immune animals is capable of immunizing other animals, and if given in sufficient strength and dose, even of arresting the disease when already established. The tendency at present is to ascribe the causation of immunity to a peculiar property of the body-fluids whether bactericidal or antitoxic in nature, i. e., counteracting the bacterial poison; this is not fully established.