Page:The Harveian oration 1888.djvu/22

14 to a good deal of discussion. These rod-shaped bacilli have been shown to exist, in all cases of human tuberculosis, in the sputum, in caseating scrofulous glands, and in the tubercular masses in the lungs. Pure cultivations of these bacilli when introduced beneath the skin of susceptible animals such as rabbits, guinea- pigs, cats, and field-mice, always produce after three, four, or more weeks, the typical tubercular lesions; swollen lymphatic glands, deposits in the spleen, liver, and lungs, and enlargement and caseation of the bronchial glands. Different species of animals present very different degrees of susceptibility; the domestic mouse is not easily affected, whereas the field-mouse is highly susceptible; and as eveiy practical physician knows, in certain families of the human species there is an unmistakable liability, an inborn tendency to suffer from tuberculosis, whereas other families entirely escape. Wherein lies this great difference of susceptibility"? In what way do the micro-organisms either in tuberculosis or anthrax or relapsing-fever influence the economy? how do they produce the disease? Why should some animals resist their power and others be overwhelmed by them? Recent investigations seem to me to throw some light on these points, and in some degree to answer these questions.

When certain forms of bacilli, of the so-called non-pathogenic character, are introduced into the blood of the lower animals, even in large numbers, their existence is of comparatively short duration, and they speedily disappear. The living blood has the power of destroying them. In three hours according to Wysso-kowitsch none are present even though enormous numbers are injected. They are deposited in the liver, spleen, and medulla of bone, and soon die if they do not contain spores. If spores are injected these live much longer, those of bacillus subtilis being still