Page:Popular Science Monthly Volume 41.djvu/849

Rh. Altogether, some substances exercise upon leucocytes a decidedly attractive power, while other substances repulse them.

As to what happens with microbes which have been ingested by leucocytes, the result may be very different in various conditions. The red corpuscles of blood, when ingested by leucocytes, are digested; globules of pus and fragments of muscular tissue also are digested by means of a special ferment (discovered in 1890 by Rosbach). And the same happens with microbes if the leucocytes of the organism are healthy and the animal is refractory to a given disease, either from natural causes or in consequence of vaccination. The bacilli of anthrax are undoubtedly destroyed by the leucocytes of the dog, as well as by those of such rabbits as have been vaccinated against anthrax. If the leucocytes are healthy, they prevent the germination of the spores which they have ingested; but they maintain this power so long only as they are healthy; because, if the animal has been submitted to cold (or to heat in the case of a frog), or if it has been narcotized, it loses its immunity. Moreover, the very affluence of phagocytes to an infected place may be accelerated through nervous action, or slackened by various narcotics.

Such being the facts, it was quite natural to explain them, as Metchnikoff did, by maintaining that the phagocytes are the natural means of defense of organisms against infectious disease. The very necessities of struggle for life have evolved this capacity of the organisms of protecting themselves by sending armies of phagocytes to the spots attacked by noxious micro-organisms. The struggle may evidently end in either the defeat of the phagocytes, in which case disease follows, or the defeat of the microbes, which is followed by recovery; or, the result may be an intermediate state of no decisive victory on each side, as is the case in various chronic diseases.

As to the force which attracts the leucocytes toward the microbes, it is already indicated by the extensive researches of the other school, which has devoted its chief attention to the chemical aspects of infection. It may be, as it is maintained by