Enemata are rectal injections employed to evacuate the bowel, to influence the general system by absorption, or to affect locally the seat of disease. Enemata which are intended to evacuate the bowel are usually given in large bulk (1 to 2 pints) injected slowly by means of a Higginson's syringe, or from a douche-can. Care should be taken to avoid the introduction of air, by filling the syringe or tube with the enema before starting to inject. Enemata which are intended to be retained in order that absorption may take place do not usually exceed 5 fluid ounces in volume for adults, smaller quantities being used for children. Retention is favoured by very slow administration, preferably by means of a soft catheter passed well into the bowel. Enemata should be given at a temperature of about 38°. Enemata for lavage of the mucous membrane of the large bowel are passed into the colon by means of a long indiarubber tube.
Substances which are absorbed unaltered when taken by the mouth are usually taken up with equal facility per rectum. Albuminoids are not readily absorbed, but peptones, albumoses and sugars are efficient rectal aliments. Skin rashes sometimes follow repeated rectal injections.