Rose and Carless's manual of surgery for students and practitioners.

  • William Rose
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: Rose and Carless's manual of surgery for students and practitioners. Source: Wellcome Collection.

    29/1454 (page 17)
    Active immunity is usually much more lasting, though its duration varies greatly in different cases. In most cases of syphilis and small-pox it is permanent, second attacks being extremely rare, whereas in pneumonia and erysipelas it is of very short duration. When we turn to the theories which have been promulgated to explain the facts briefly outlined above, it must be borne in mind that there are two groups of phenomena which require elucidation: the immunity to the bacteria and the immunity to their toxins. Thus, if a culture of living diphtheria bacilli is injected together with their toxin into a susceptible animal, the bacilli will continue to grow in its tissues, and the toxin will exert its poisonous effects, both local and remote. If the same culture is injected into an immune animal (whether the immunity is natural, active, or passive), the bacteria will be killed and the toxin will have no action. This bacterial immunity must first be discussed. Omitting theories which are merely of historical interest, we come first to the humoral theory, which asserts that the destruction of the bacteria is due to certain substances which are present in the blood, lymph, etc., and which are designated alexins. The ex¬ perimental foundation for this theory consists in the fact that fresh blood, and more especially fresh blood-serum, has very consider¬ able bactericidal action. This action is destroyed if the serum is exposed to heat (about 6o° C. for half an hour), and disappears spontaneously after a day or so; when the alexins have been destroyed by either process, the serum becomes an excellent culture medium for most bacteria. Metchnikoffs theory of phagocytosis (the cellular theory) was at first in strong opposition to the humoral theory, but subsequent researches have brought the two closer together. Starting from the fact that unicellular protozoa (such as the amoeba) ingest, digest, and assimilate the bacteria found in water, Metchnikoff was led to examine the action of the leucocytes, or wandering cells of the higher animals, which in their morphology so strongly resemble the lower protozoa, and found in them a similar power of engulfing and digesting living micro-organisms. This process he termed phagocytosis. A striking example occurs in Daphnia (the fresh-water flea), an animal which is so transparent that the whole phenomenon can be followed under the microscope during life. It is affected with a disease due to the growth in its tissues of a fungus known as Monospora. The spores of this parasite are taken in with the food, and penetrate from the alimentary canal into the body cavity; when unchecked, they continue to grow until the whole animal is filled with growth. If, however, but few spores gain access, the defensive mechanism comes into play, and the spores are surrounded and engulfed by the leucocytes, submitted to a process of digestion, and finally destroyed. It is obvious that Daphnia is partially immune to Monospora, and that the immunity depends on the phagocytic activity of its leucocytes. Metchnikoff had no difficulty in finding many examples of the same process in