Manual of surgery for students and practitioners / byWilliam Rose.

  • Rose, William, 1847-1910.
Date:
1908
Catalogue details

Licence: Public Domain Mark

Credit: Manual of surgery for students and practitioners / byWilliam Rose. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    very severe, indicating a very high degree of virulence in the organism. In general, we know little or nothing of the causes which lead to increase of virulence under natural conditions. The outbreak of an epidemic of small-pox, for instance, must be due to a sudden increase in virulence of the specific organism, but the causes which lead to this are quite obscure. Cultures of an organism of diminished virulence are said to be attenuated; thus vaccine is a culture of the unknown small-pox organism in an attenuated state. The artificial attenuation of patho- genic bacteria is a subject of great importance in connection with the production of immunity, and it may be laid down as a general rule that the cultivation of an organism under slightly disadvantageous con- ditions tends to diminish its virulence, and vice-versa. For example, the anthrax bacillus grows best at 370 C, or thereabouts, and retains its virulence for long periods at this temperature, but if it is culti- vated at 420 C. it becomes attenuated. Cultures thus treated con- stitute Pasteur's vaccine against anthrax ; when injected into animals they cause transient ill-effects, but the animal becomes immune to the disease. (3) The organism must be pathogenic, if infection is to occur, and by this we mean capable of producing disease in the animal in question. Thus, the inoculation of the gonococcus into the urethra of animals leads to no results, and infection does not take place. Hence two factors must be present: the organism must be virulent, and the host susceptible. (4) Lastly, an essential feature of infection is that the toxins of the organism must act on the tissues of the host. Thus, it is quite possible, and not uncommon, for streptococci to be present in the outer layers of the skin, and the B. diphtheria in the mouth, etc., and yet for no harmful effects to arise, since either the organisms do not form toxins, or else these toxins do not reach the tissues. This is not infection, although in such cases any slight lesion or any condition leading to local or general lowering of resistance may bring it about. The terms specific and non-specific as applied to infectious diseases also require explanation. A specific disease is defined as one which is produced by a single cause—i.e., a particular species of micro- organism, and by no other. Thus, tetanus is a well-marked patho- logical entity, always due to the B. tetani, and may be taken as the type of a specific infection. Suppuration, on the other hand, may be caused by a large number of species of bacteria, or even by chemical irritants, and is therefore termed non-specific. The boundaries of these divisions are constantly changing with the advancement of pathological research. The common process is for diseases which are apparently homogeneous to be split up into groups of specific diseases, each due to its own organism. Thus, ringworm is now known to be due to several different forms of fungus, and combined clinical and pathological research have shown that the diseases due to one variety differ in minute points from those due to another.