(1) They have a local action, as, for example, in the formation of an abscess. The presence of the causal bacteria in the tissue brings about very marked changes. There is a multiplication of connective-tissue corpuscles, an emigration of leucocytic cells, a congestion of blood corpuscles. All these elements assist in creating a swelling and redness, and pain by the subsequent pressure upon the delicate nerve endings. These, as we all know, are the symptoms of a "gathering" or abscess. It is a "gathering" in a strict pathological sense--a gathering of cells to oust the intruder or build around it a wall or capsule as a protective measure. Now the toxin will commence its local action. The oldest cells in the mass of congestion will be caused to break down into liquid; what is called a _necrosis_, or death, will rapidly set in; and we shall have the connective-tissue cells, leucocytes, blood corpuscles, etc., losing their form and function, and "coming to a point" as matter, or _pus_. The local breaking down of these gatherings of cells into fluid matter is believed to be the work, not of the bacteria themselves, but of their toxins. (2) Toxins may be absorbed and distributed generally throughout the body. They produce degenerative changes in muscles, in organs, and in the blood itself. Let us take diphtheria as an example. The bacillus occurs in a false membrane in the throat and occasionally other parts. It causes first the inflammatory condition giving rise to the membrane, and then it breaks it down. In the body of the membrane the bacillus appears to secrete a ferment which by its action and interaction with the body cells and proteids, chiefly those of the spleen, produces _albumoses_ and an _organic acid_. These latter bodies are the toxins. They are absorbed, and pass throughout the body. There are albumoses, therefore we get the frequent pulse and high temperature of fever; the toxins irritate the mucous membrane of the intestine, and cause various fermentative changes in the contents of the intestine, therefore we get the symptoms of diarrhœa; they penetrate the liver, spleen, and kidney, therefore we get fatty degeneration and its results in these organs; they finally affect many of the motor and sensory nerves, breaking up their axis cylinders into globules, and therefore we get the characteristic paralysis. Loss of weight naturally follows many of these degenerative or wasting changes. Here, then, we have some of the chief changes set up by the toxins, and these changes constitute the leading symptoms in the disease as it is known clinically.