Quotation from: Manual of SurgeryWritten by: Alexander Miles and Alexis Thomson |
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#Pathogenic Properties of Bacteria.#--We are now only concerned with pathogenic bacteria--that is, bacteria capable of producing disease in the human subject. This capacity depends upon two sets of factors--(1) certain features peculiar to the invading bacteria, and (2) others peculiar to the host. Many bacteria have only the power of living upon dead matter, and are known as _saphrophytes_. Such as do nourish in living tissue are, by distinction, known as _parasites_. The power a given parasitic micro-organism has of multiplying in the body and giving rise to disease is spoken of as its _virulence_, and this varies not only with different species, but in the same species at different times and under varying circumstances. The actual number of organisms introduced is also an important factor in determining their pathogenic power. Healthy tissues can resist the invasion of a certain number of bacteria of a given species, but when that number is exceeded, the organisms get the upper hand and disease results. When the organisms gain access directly to the blood-stream, as a rule they produce their effects more certainly and with greater intensity than when they are introduced into the tissues.
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