l6 PHARMACEUTICAL BACTERIOLOGY. 



immunity, race immunity, animal immunity, individual immunity, artificial 

 immunity, natural immunity, acquired immunity, etc., attracted attention 

 and received careful consideration. Metchnikoff (1884) explained im- 

 munity on the supposition that certain white corpuscles (leucocytes, phago- 

 cytes) of the blood devoured the microbes which entered the system. These 

 white blood corpuscles are the guardians of health. They attack and feed 

 upon any disease germs which may enter the body, either via the digestive 

 tract, the respiratory tract, or via the circulatory system. If the leucocytes 

 are deficient in number, or if the microbes are excessive in number, disease 

 will develop. This theory had numerous followers, as well as opponents. 

 It is now generally accepted as correct, borne out by observation and by 

 experimental evidence. 



The next important discovery was that blood serum had bactericidal prop- 

 erties in a varying degree, and that in addition to this there was something 

 in the blood which had a tendency to neutralize or destroy the action of the 

 poisons or toxins formed by pathogenic microbes. No one particular 

 bacteriologist can be said to have made these discoveries. We can only 

 name a few of the leading investigators who worked along these lines, leading 

 to the discovery of the relationship of immunity and antitoxins — Behring, 

 Brieger, Buchner, Calmette, Chamberland, Ehrlich, Emmerich, Flugge, 

 Frankel, Hueppe, Jetter, Kitasato, Klemperer, Loffler, Rankin, Roux, 

 Wassermann, and others. These eminent authorities have demonstrated 

 the possibility of developing or aiding the antitoxic or immunizing power 

 of the blood or of the body cells by introducing sera obtained from the blood 

 of animals in which the antitoxic power is naturally high or is made so as 

 the result of special treatment. Numerous sera (containing antitoxins and 

 toxins) were tried; the one which first proved entirely satisfactory was the 

 diphtheria antitoxin of Behring, which is now in universal use. Others 

 are used more or less successfully, and some are still in the experimental 

 stage. 



In 1890 Koch reported on a "lymph" to be used in the treatment of 

 tuberculosis. This lymph was a glycerin extract of the toxin of the bacillus 

 of tuberculosis, and was to be used in the treatment of this dread disease, but 

 the hopes of Koch were not realized, as the remedy proved a failure, and it 

 soon fell into disuse, to be again taken up very recently. In 1907 Wright 

 made known his discovery of opsonins. According to this authority, there 

 exist in the blood certain substances which have the power of acting on the 

 invading bacteria in such a manner as to render them more liable to be 

 attacked and assimilated by the white blood-corpuscles or leucocytes. There 

 are possibly as many opsonins as there are microbes capable of being di- 

 gested by the leucocytes. The microbe-devouring power of the leucocytes 

 can be increased by the use of bacterial vaccines, which consist of suspensions 



