g up the
oxygen of the blood. Such action is now known to be quite a subsidiary
matter. And although effects may sometimes be produced in a mechanical
manner by bacteria plugging capillaries of important organs, _e.g._ brain
and kidneys, it may now be stated as an accepted fact that all the
important results of bacteria in the tissues are due to poisonous bodies or
toxins formed by them. Here, just as in the general subject of
fermentation, we must inquire whether the bacteria form the substances in
question directly or by means of non-living ferments or enzymes. With
regard to toxin formation the following general statements may be made. In
certain instances, _e.g._ in the case of the tetanus and diphtheria
bacilli, the production of soluble toxins can be readily demonstrated by
filtering a culture in bouillon germ-free by means of a porcelain filter,
and then injecting some of the filtrate into an animal. In this way the
characteristic features of the disease can be reproduced. Such toxins being
set free in the culture medium are often known as _extracellular_. In many
cases, however, the filtrate, when injected, produces comparatively little
effect, whilst toxic action is observed when the bacteria in a dead
condition are used; this is the case with the organisms of tubercle,
cholera, typhoid and many others. The toxins are here manifestly contained
within the bodies of the bacteria, _i.e._ are _intracellular_, though they
may become free on disintegration of the bacteria. The action of these
intracellular toxins has in many instances nothing characteristic, but is
merely in the direction of producing fever and interfering with the vital
processes of the body generally, these disturbances often going on to a
fatal result. In other words, the toxins of different bacteria are closely
similar in their results on the body and the features of the corresponding
diseases are largely regulated by the vital properties of the bacteria,
their distribution in the tissues, &c. The distinction between the two
varieties of toxins, though convenient, must not be pushed too far, as we
know little regarding their mode of formation. Although the formation of
toxins with characteristic action can be shown by the above methods, yet in
some cases little or no toxic action can be demonstrated. This, for
example, is the case with the anthrax bacillus; although the effect of this
organism in the living body indicates the production of toxins wh