This section is from the book "Diseases Of The Intestines", by Max Einhorn. Also available from Amazon: Diseases Of The Intestines A Text-Book For Practitioners And Students Of Medicine.
Undigested remnants of food, macroscopically visible, occur in the faeces. Normally, however, only small particles of vegetable substances, like potatoes, asparagus, spinach, peas, etc., are found, while remnants of meat can never be discovered with the naked eye. In case particles of meat are visible, it indicates a severe lesion of the intestinal tract. If large amounts of undigested food (even vegetable matter) are present in the faeces, it is also an indication of an existing severe lesion.
Abnormal admixtures frequently occur in the faeces, and are occasionally of great diagnostic importance. Thus, blood may be found either in its fresh condition (red) or it may be very dark but not coagulated. In both instances the blood comes from the lower portions of the large bowel. Sometimes the blood appears in a more changed and decomposed form, giving the faeces the appearance of tar. In this instance it priginates from the higher portions of the bowels or from the stomach.
An admixture of pus in the dejecta which can be macroscopically recognized occurs only in instances in which pus exists in the lower portions of the large intestine. For if there is pus present in the higher portions of the bowel, it is usually changed before its exit in such a manner that it cannot be detected unless the amount is very considerable.
Mucus, although a normal constituent of the faeces, cannot be discovered in large amounts under physiological conditions. Macroscopically visible mucus may exist in the following forms: (1) It may surround the fecal matter in the form of a glassy layer. This usually indicates a diseased condition of the lower portion of the bowel. (2) The mucus may appear in the form of membranes and may be evacuated either alone or after a fecal evacuation. This often occurs in membranous enteritis. (3) The mucus may appear in a mushy movement having a yellowish coloration and be well mixed with faeces. If a glass rod is dipped into such an evacuation the mucus adheres to it. (4) The mucus exists in small particles visible with the naked eye and floating in the watery dejecta. All these varieties of mucus with the exception of (2) indicate the presence of a catarrhal condition of the intestine.
Intestinal parasites also occur in the faeces, and their discovery may elucidate the diagnosis.
The reaction of the faeces is normally neutral or slightly alkaline. Under a diet rich in vegetables, however, it is slightly acid. In cases in which there is an occlusion of the bile duct so that it does not empty into the intestines the reaction is strongly acid. The test for the reaction is best made by means of litmus paper. The reaction at the surface of the fecal matter may be different from that in the interior. It is therefore best to test both.
The amount of acidity or alkalinity of the faeces can be determined by mixing 10 to 20 c.c. of the fresh fecal matter with about 100 c.c. of distilled water. A drop of a phenol-phthalein solution is added and as much of a decinormal solution of either sodium hydrate or sulphuric acid until the red color appears, or if the alkalinity has to be determined, disappears. The reaction of the faeces is, however, not of much diagnostic value.