We have considered a chain of events by which disease is produced without the intervention of any secondary cause. Such a condition may be called, for convenience, a simple subluxation disease. Its existence depends directly upon the subluxation which is the first change manifest in the individual and upon which all the other changes depend. The two facts that not all subluxations impinge nerves and not all nerve impingements cause demonstrable disease explain why we do not, in practice, find a disease to correspond with each subluxation discovered by palpation. It must be remembered that there may be latent weakness following a subluxation and of importance because it renders the patient susceptible to infection or to the action of other secondary causes. SECONDARY CAUSES Among the secondary causes of disease may be mentioned the pathogenic germ, poisons, dietetic errors, abnormal mental states, bodily excesses, exposure to sudden temperature changes, and inhalation of non-poisonous but irritating substances as the most common. Many others might be included but these will suffice for complete illustration of the principle. It will be our endeavor to show how each of these secondary causes operates by virtue of a previous susceptibility, or breaking down of the normal resisting power of the organism caused by subluxation, and how each in turn _may_ bring about increase in subluxation and thus, both directly and indirectly, increase disease. Bear in mind these two all-important facts. _None of these secondary causes can operate without previous subluxation. A subluxation may produce disease without the aid of any secondary cause._ GERM DISEASES These comprise a large portion of the febrile affections. Most germ diseases are characterized by fever and the presence of circulating toxins with resulting disturbance of the metabolic processes of the body. It is generally agreed among pathologists that the greater number of varieties of micro-organisms found at times in man are not pathogenic. Some aid in the decomposition of food in the alimentary canal; others have various beneficial functions to perform. But some, under proper conditions, feed upon and destroy living tissue. These are the so-called pathogenic germs. The pathogenic germs are many. They enter the body by various routes, in the air we breathe, the food we eat, the water we drink; sometimes they are communicated by direct contact with other persons or with objects infected with them. The term “contagious” is applied to those diseases whose germs may be carried through the air from one to another; “infectious” refers to those communicable only by contact.