The means of aggression or defense, as well as of sustenance, of the phagocyte, is by attaching itself to a particle of matter, and gradually surrounding and incasing it in its membranous walls until it is literally swallowed. If the particle should be a microbe, rich in protoplasm, it would be digested by the voracious and omnivorous phagocyte; but if of mineral origin, as dust of coal or sand inhaled by the lungs, it would be carried to the surface or to a safe receptacle, where the cell, having performed its mission, deposits itself, still incasing its burden. The phagocytes seem to meet whole broods of infective microbes which may have invaded the body, and destroy them, and, as it were, gradually acquire and permanently retain such efficiency as in future invasions of the same species to prevent any harmful action. The contest between these opposing forces does not always terminate with regularity as to time, as in the acute infectious diseases, but may become chronic, and the time and result uncertain.
In the slow, malarial diseases, according to this theory, the phagocytes finally acquire a domination more or less complete over the Bacilli malariæ; and this occurs not because the malaria has become less virulent, but because the phagocytes have acquired unwonted potency during the contest. This acquired domination of the phagocytes over one species of microbe seems not to be available against the inroads of other species. The exemption acquired in diphtheria and some other diseases seems partial as to degree and uncertain as to time.
One dreadful example of the failure of self-limitation of disease is found in hydrophobia. Here there is no natural stay or check to its fatality, and, although the most distinguished pathologists have given this question their best attention for many years, it seems questionable whether any life has ever been saved from hydrophobia. Large numbers of persons have been treated by inoculation for supposed hydrophobia, many of whom died, and the symptoms proved the hydrophobic cause; while in those who recovered no positive demonstration of true hydrophobia could be made, and the question of curability or prevention by inoculation remains undetermined.
M. Pasteur, the wizard micrologist, claims success in his battles with the rabies germs, and his brilliant achievements in other fields lend encouragement to expectant humanity. Jenner's vaccine discovery, by which millions of lives have been saved, encourages the sanguine belief that the principle of inoculation will, ere long, be made available for the preservation of countless human lives.
The method of M. Pasteur has been to obtain some of the positively fatal virus from the brain of a person or animal which