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JAMA 100 Years Ago
August 17, 2005


Author Affiliations

JAMA 100 Years Ago Section Editor: Jennifer Reiling, Assistant Editor.

JAMA. 2005;294(7):855. doi:10.1001/jama.294.7.855-b

The editorial in THE JOURNAL, August 5, entitled “Declining Virulence and Advancing Parasitism” has caused a correspondent to call our attention to an article that appeared in THE JOURNAL, May 3, 1890, written by Bayard Holmes of Chicago, in which infectious parasitism is discussed from the same general point of view, i. e., the evolutionary, as in Theobald Smith’s address. When Holmes wrote his article our knowledge of the finer mechanisms of the establishment and healing of bacterial infections was in its very beginning; the life history, the mechanisms of ingress and egress, the distribution of most of the pathogenic microbes were as yet largely unknown. Consequently it was only the grosser facts of parasitism and of infection that could be used to construct any theories as to the evolution of infection, and this it must be said that Holmes did with great skill and farsightedness. After reviewing certain of the general facts of parasitism and especially those that indicate that the obligate parasites of tuberculosis, syphilis, measles, scarlet fever, etc., must have occupied long periods of time to become adapted to their present very restricted modes of existence, Holmes asks how has it been possible for man to withstand the attacks of so many enemies for so long a time? He answers that the reason is that the parasites were not essentially destructive; had they been so, neither host nor parasite would have survived; for with the destruction of the host species occurs the destruction of the parasite. The diseases mentioned may become more or less destructive, however, by virtue of secondary mixed infections and other accessory factors, such as all that tend to weaken the body. In the case of facultative parasites, on the other hand, the chances, so Holmes argued, are more against the host in the conflict that ensues, because natural selection has not rendered us indurate to them. It will be seen that Smith’s theory goes much farther than Holmes’ in that the former includes under his law of declining virulence and advancing parasitism, not only obligate parasites, but also the facultative invasive microbes, i. e., those that appear to be slowly moving, through long periods of time, toward higher degrees of parasitism.

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