As I have already shown, the action of a saline purgative on the intestine consists of two parts, the increase of the peristaltic activity and the increase of the amount of fluid secreted into the lumen; or, in other words, the action on the muscle and the action on the glandular tissue. In the experiments just described it is clear that these two separate actions exist side by side. For example, m/8 solutions of sodium chloride, citrate, or sulphate cause well marked peristaltic movements or allow these to continue, while no secretion of fluid takes place. Stronger solutions of these salts, on the other hand, such as m/2 produce a distinct secretion. Thus a concentration of a salt which is sufficient to produce muscular activity may not be sufficient to affect the glandular tissues. One is tempted to conclude that in the intestine it requires a stronger stimulus to produce secretory activity than it does to cause muscular movements. It is possible that this is true, but the anatomical relations also must be taken into consideration. The muscle coats lie immediately under the thin peritoneal layer through which the salts are absorbed; and it seems probable that in the experiments described the solutions reached the muscle more easily and rapidly than they could the glandular tissue which is situated on the other side of the muscular and submucous layers. Further, it must be noticed that the movements seen in m/8 NaCl may be merely the continuation of those caused by separation of the loop from the central nervous system. The amount of fluid which may be secreted by a loop of intestine isolated from the body is limited by the absence of the blood supply. The loop, as shown above, secretes a certain amount of fluid in the first 10 or 20 minutes. If it is then emptied, usually no more fluid appears. The quantity secreted depends on the amount of fluid contained in the intestinal walls at the time of its removal from the body. No fluid passes from the solution in which the loop is suspended into the lumen of the loop; no current is established through the walls from the outside inwards. It seems possible to supply the stimulus for secretion in the solution in which the loop is suspended; but it is not possible in this way to renew the fluid which the glands have secreted into the lumen. This can apparently be done only through the blood vessels. FOOTNOTES: [60] MACCALLUM, J. B.: University of California Publications, Physiology, Vol. I, 1904, p. 115. CHAPTER VII. The Action on the Intestine of Solutions Containing Two Salts.