In 1888 Pasteur advanced the exhaustion theory wherein he maintained that the body which had no food for the germ to feed upon would be immune; in other words, when the food supply was used up the germ could no longer develop and grow. An illustration of this is the yeast which will cease to grow when the sugar in the culture media is exhausted. This theory was rejected but has since been revived and is now considered to have some merit. This theory comes very nearly agreeing with the chiropractic idea, which will be discussed later. Retention Theory Another theory is that of Chaveau, which is known as the retention theory. This is just the opposite of the exhaustion theory and maintains that the products of metabolism within the microörganisms, the excreta of the germs, form a toxin or a substance which is retained in the body of the host and protects it against the growth and development of the germs, in this way producing immunity. That which can not be used in the metabolism of an organism will naturally be excreted, for if it is allowed to remain in the body it will impair the tissues. The excreta of the germ then can not be used in its own metabolism and is therefore a poison to the germ as well as to the host. This waste accumulates until the germ eventually is destroyed by the poison of its own excreta. This is given as an explanation of self-limited dis-eases. It is further explained by this theory that this poisonous excreta of the germ is retained in the secretions of the body of the host and acts as a protection against further invasion, for when other germs of the same character enter the body they come in contact with this poison and are destroyed. In this way immunity is supposed to be maintained. But this is not logical, since the excreta of these germs can not be used in the metabolic processes of the human body. It is a poison and will be dealt with by Innate as such. Innate does one of two things when poison enters the body or when it is manufactured within the body. One is to eliminate it through the normal channels of excretion; the other is to produce an antidote in the form of an internal secretion to neutralize the poison. In either event the excreta of the germ would lose its potency as a germicide and could therefore have nothing to do with the production of immunity. Various Theories Again, it is claimed that the phagocytes perform a very important function in protecting the body against invading microörganisms by attacking, destroying and digesting them. Another theory is that the antibodies of various kinds play an important part in keeping the body free from undesirable invaders. It is also asserted that immunity is produced in a negative way by the absence of a specific affinity between the tissue cells and the toxin.