Page:The Harveian oration 1888.djvu/38

30 tubercle bacillus finds a congenial home in which it spreads and thrives and multiplies.

Again, the condition often seen in some parts antecedent to the formation of tubercles in the human system indicates that there is often some structural change before the bacilli take possession of the part, and "that their appearance on the scene is subsequent to the damage of which they are in fact the pathological consequences." Not infrequently, in cases of acute tuberculosis of other organs we find an affection of the membranes of the brain presenting all the characters of simple inflammation, no tubercles being discoverable. And iu the lungs the first stage of the morbid process is of a similar character, namely the filling of the alveoli with epithelial cells, or in other words a "catarrhal pneumonia." And according to the vitality of these epithelial cells will be the changes produced in them by the bacilli. Some of the cells possessing greater vitality will, when attacked by the bacilli, go on increasing or coalescing, and so, in some way or other, the formation of the so-called ** giant cells " takes place, which at one time were regarded as the typical elements of tubercle, and the remarkable phagocyte property of which has been recently shown by Metschnikoff to be something more than a theory. If the cells are of a weaker nature they quickly die and undergo degeneration, and become caseous.

And, once again, it may be suggested that when the bacilli have gained a footing in this effete or enfeebled tissue, whilst absorbing from it the constituents of their own protoplasm, they may give rise to, or secrete, poisonous products or ferments, capable of still further destroying or weakening the surrounding tissue or cellular elements and so obtain fresh food on which they can thrive. In this way, to use Dr Sanderson's words :