Before closing this chapter we must also briefly insist upon the importance of the fact, that the secretions of the intestine and of its glandular annexes have also an anti-bacterial and antitoxic action. Very important is the rôle of the bile for the disinfection of the intestine, as it contains two acids, the glycocholic and taurocholic, which possess highly anti-fermentative properties. As already mentioned, the bile also assists in the assimilation of fat, and also exercises a stimulating action on the peristalsis of the intestines. ------------------------------------------------------------------------ CHAPTER XVIII. ON THE PREVENTION AND TREATMENT OF HABITUAL CONSTIPATION. WE all know from physiology that the expulsion of fœcal matter from the intestines takes place in such a manner that the contents therein act as a kind of _extraneous_ body with stimulating action upon the walls of the intestines and the plexus myentericus contained in the same. Consequently there follows a contraction of the walls of the intestines, and their contents are expelled. All nerves, the plexus myentericus included, are under the control of the central nervous system, which creates motor impulses through the medium of the pneumogastric (vagus), or may cause a check to the peristaltic movements through the intervention of the splanchnic nerves. Thus, as we see, different agencies influencing the central nervous system, like strong emotions, shock, etc., may cause an irritation of the pneumogastric, the motor nerve of the intestines, and thus occasion a movement of the bowels. Different toxic products may act also upon the pneumogastric; strong motor action of the intestine with diarrhœa may also be caused by the abundant secretion of the thyroid gland, as in Graves’s disease, where an excess of toxic matters of the thyroid gland are secreted. In the same way we can also produce diarrhœa if we give thyroid extracts in too abundant quantity; but giving the same in more moderate doses will effect an improvement in the peristaltic movements. That the thyroid gland has a controlling influence on the innervation of the intestine is evident from the fact that, when the thyroid is degenerated, the bowels are very sluggish. Under such conditions we often find very stubborn constipation; but when we administer to such persons thyroid extracts for a given time, we note a considerable improvement of the bowels, which can even go to the extent, if too excessive doses be given, of causing diarrhœa as already mentioned.