In studying the natural history of the large intestine, it striking that this portion of the gut is well developed only among mammals. These animals, for the most part, lead an extremely active terrestrial life. Most of them have to move about very quickly, the predacious forms in pursuit of their prey, the herbivorous forms to escape from their enemies. In such a mode of life, the need to stop in order to empty the intestines would be a serious disadvantage, and the possibility of retaining the dejecta in a large reservoir would be very useful.[81] Such are the causes that have determined the growth of the large intestine among mammals. Birds, which live, so to speak, in the air, and which do not need to arrest their locomotion in order to void their excreta, have no large intestine. Reptiles and amphibia, although they live a terrestrial life, do not require a voluminous large intestine, and such is not found among them. These animals do not have a fixed temperature; they are what we know as “cold-blooded,” and in consequence are small eaters. Most of them are sluggish, and do not lead an active existence like that of mammals. In the legacy acquired by man from his animal ancestors, there occur not only rudimentary organs that are useless or harmful, but fully developed organs equally useless. The large intestine must be regarded as one of the organs possessed by man and yet harmful to his health and his life. The large intestine is the reservoir of the waste of the digestive processes, and this waste stagnates long enough to putrefy. The products of putrefaction are harmful. When fæcal matter is allowed to remain in the intestine, as in cases of constipation, a common complaint, certain products are absorbed by the organism and produce poisoning, often of a serious nature. Every one knows that a high temperature may be the result of constipation in women after childbirth, or in patients recovering from an operation. This is due to an absorption of substances produced by the microbes of the large intestine. Similar products may be the cause of an attack of acne or of other skin diseases. In fine, the presence of a large intestine in the human body is the cause of a series of misfortunes. The organ is the seat of many grave diseases, among which dysentery is notable. In some tropical climates dysentery is a serious scourge. According to Rhey,[82] it is “the greatest danger to which a European is subjected in Tonkin. It is responsible for more than 30 per cent. of the deaths caused by disease.” European troops pay it a large annual toll in the colonies of the French and English.