Special mention may be made of two procedures calculated to pre vent the development and spread of diphtheria. Children can easily be instructed to allow inspection of the pharynx peaceably and willingly and this should be done daily in times of epidemics. They may also be taught to gargle, so as to bathe the posterior pillars and pharyngeal wall, and then in times of epidemics this may be done twice daily with a disinfecting solution, preferably with peroxide of hydrogen.
The entrance of the diphtheria toxin into the body does not have wholly harmful results, for it also stirs up a reaction by which not only the circulating toxins become destroyed, but also the organism remains immune, protected for a longer or shorter period of time against the harmful action of the specific poison.
The condition of specific immunity may be produced experimentally in animals. If a non-fatal dose of diphtheria toxin is injected into an animal, that animal, after showing symptoms of the disease, becomes immune to a much greater close of the toxin. By means of regulated injections of steadily increasing amounts of the toxin it is possible finally to produce an immunity to any number of times the former fatal dose (active immunity).
If the serum of an animal so treated is injected into another ani mal, this second animal shows itself resistant to a subsequent introduc tion of the toxin (passive immunity); indeed, the serum from the first animal shows not only a protective action, but also a healing one, so that when injected into an animal the subject of diphtheria, it brings the disease to a standstill, modifies it and hastens recovery. For this healing action, much greater amounts of the serum are necessary than to produce the protective action, and so much the greater, the further the disease has advanced.
On this possibility of transferring the protective and healing action of the serum of an artificially immunized animal not only from animal to animal but from lower animals to man, rests von Behring's serum therapy of diphtheria.
Inasmuch as natural and artificially acquired immunity may be transferred by means of the blood and its derivatives, there must be con tained in the latter specific protective substances, antibodies. Whether these exist preformed in the body or are newly developed is a mooted point. To explain the action of the antitoxin on the toxin there have been advanced three theories: a physicochemical theory (Arrhenius and Madsen), a physiological (Ehrlich), and a biological (Pauli).
Explanation of Natural and Artificially Acquired iumunity.—Accord ing to Ehrlich and von Behring that substance which naturally in the cells is greatly increased in amount by the action of the toxin, becomes the primary cause of healing when it is given off by the cells into the plasma of the blood.
According to Arrhenius and Madsen, the saturation of toxin and antitoxin is really a dissociation of combinations with weak affinity (Dieudonne).
According to Pauli, the toxin and antitoxin have colloidal charac teristics and the very varied reactions of immunity are changes of the colloidal condition, a more or less complete neutralization of colloidal solutions (W. Pauli).
The antitoxic serum is mainly derived from horses which have been highly immunized to diphtheria. The value of the serum is found by its action toward a solution of the diphtheria toxin of known strength. That amount of serum capable of neutralizing one hundred times the fatal dose for a guinea-pig is called an antitoxin unit. If this activity is contained in one cubic centimetre of serum, that serum is called one fold serum, but if it is contained in the hundredth part of a cubic centi metre, the scrum is called 100-fold. At the present time, serum of a strength 400- and 500-fold is in the market.
In America, serums of greater concentration than those mentioned are to be found in the market. Natural serums of 700—S00-fold are obtainable as are also equally strong serums which have been concen trated by chemical means. Gibson has worked out a process by which the serum globulins, with which the antitoxic principle is identified, are separated from the serum albumins and the other globulins. These antitoxic globulins are soluble in an amount of physiological salt solu tion from one half to one third the volume of the serum from which they are derived. In this way serums can be concentrated from two to three fold. Moreover it has been shown by Park that by the use of this concentrated and purified antitoxic globulin solution only about one half the number of cases of the "serum sickness" result and its severity is much diminished.