INTROSPECTION. 723 INUNDATION. them. It means that, with the, advent of experi- mental control, psycholcj.'j' was able to combine Uie altitude of inner perception with the plan and system of self-observation; and that this ■ science thus acquired a method which is as ac- curate and relial)le in principle as are the meth- ods of the physical sciences. Experiment enables us so to regulate external conditions that a de- terminate mental occurrence may be induced at a determinate moment of time; it enables us, fur- ther, to prevent any modification of conscious- ness save by the occurrence under investigation. Given a state of eonientrated attention (q.v. ) on the part of the observer, the requisite degree of practice, a retentive memory (q.v.), and an adequate command of language wherewith to report the experience (see Discrimination, Sensible I — and there is no reason why a psycho- logical introspection may not be as exact as an observation in chemistry or physics. BiOLiouRAPiiY. Wundt, Orundsiige der physio- logischen I'siirhologie, vol. i. (Leipzig, 1893) ; id.. Essai/s (ib., 188.>) : id.. Outlines of Psy- chology, trans, by Judd (ib., 1897) ; .James, Prhi- ciples of I'syrhology ( Xew York, 1890). For rules of introspection, general and special, con- sult: Kiilpe. Outlines of Psychology (New York, 189.5) ; Titchener, Outline of Psychology (ib., 1S99I : id.. Experimental Psychology (ib.. 1901). See Socwi, Psychology. INTRUSION (ilL. intrusio, from Lat. intru- dor, to thrust in, from in, in + trudere, to thrust; connected with OChurch Slav, truzdati, to tor- ment, and probably with Goth, yriartan, AS. J>rt(#aH, OHG. -driozan, Ger. -driessen, to vex), lu English law, an unlawful entry upon a free- hold estate, not at the time in the actual seisin of the ri^rhtful owner, and with the view of ousting him of his estate. It could be effected in the interval between the death of a tenant in fee and the actual entrj- of the heir, or between the death of a tenant for life and the entry of the remainderman. Though not technically classed as a disseisin (q.v.), it had similar effects, vesting the seisin and title in the intruder. The usual remedy for an intrusion was by a writ of entry. Tlie distinction between the several kinds of ouster (q.v.), dependent upon the time or manner in which it was effected, has generally been abolished in England and the t'nitcd States, and the whole subject com- prehended under the description of adver.se pos- session and di.sseisin. In Scotch law the term is employed in a looser sense to describe a trespass upon lands. INTtriTION. See Instinct. INTTJITIONISM, or INTUITIONALISM (from inluition. from ML. intuifio, immediate cognition, from Lat. inlucri, to look at, from in, in + tueri, to look). The name of the theory that our knowledge of at least some fundamental principles, wliether of metaphysics or of ethics, is due to the fact that they present themselves to us as true in their own right, and therefore need no proof of any sort. The view supposes that we have certain faculties for the Immediate apprehension of these principles; thus our intellect is supposed immediately to appre- hend the truth that two and two are four, and our conscience the truth that theft is wrong, or that action prompted by benevolence is better than action prompted by sensual appetites. In ethics, intuitionism is also used to designate the view that not general principles are immediately apprehended, but the riglitness or wrongness of each particular act. These views fail to recog- nize the fact that an unreasoned assurance of a truth may be the psychological outcome of for- gotten processes of reasoning. For an account of the origin of our knowledge of general truths, see iNDt CTioN : Knowledge, Tueoby of. INTUSSUSCEPTION (from Lat. infus. with- in + susccptio, a taking up, from suscipere, to take up, from sub, under + capere, to take), or Invagination of the Intestines. A displace- ment of a portion of the intestine into the part immediately below, just as the finger of a glove may be partly drawn within itself when the hand is withdrawn. This is a common form of intestinal obstruction occurring most frequently in infants and young children. The exciting cause is usually some irritant bringing about irregular and exaggerated intestinal peristalsis. Injudicious diet, the careless use of cathartics, and the presence of intestinal polyps are the common causative factors. The pathological con- ditions present are: the invagination mentioned above, and more or less inflammation in tho affected part of the intestine. The commonest site of the lesion is at the junction of the small and the large intestines. The involved portion of the intestine may measure anj'where from a few inches to as many feet. Unless promptly treated death usually results in a short time from gangrene of the intestine, perforation, and gen- eral peritonitis. In adults the invaginated por- tion of the intestine may become gangrenous, separated, and passed per rectum. Such a ter- mination is frequently followed by the forma- tion of a contracting scar, resulting in a chronic form of obstruction. The symptoms are: Violent abdominal pain, rather sudden in its onset; vom- iting of stomach contents and of biliary and fipcal matter : abdominal distention : the passage of bloo.ly mucous per rectum ; collapse ; normal or subnormal temperature. Palpation reveals the presence of a tumor: by rectal examination the invaginated gut may be felt with the finger, or it may even protrude through the anal orifice. The treatment is purely surgical, and should be prompt. A laparotomy is performed and the in- testinal displacement corrected. The prognosis is not at all bad in cases operated on early. In neglected cases the disease is almost invariably fatal. INULIN. A starch-like constituent of some plants. See Elecampane. INUNDATION (Lat. inundatio. from inun- dare, to overflow, from in, in + undarc. to rise in waves, from undo, wave; connected with OHG. undea, unda, AS. y]>, wave). Many large areas of low ground near rivers or the ocean are in danger of inundation from various causes. Of these inundations the most common, and probably also the most destructive, are the river floods that result from unusual rains or melting snows. Most rivers are subjected to rising and falling by these causes, and those that flow through flood plains or deltas may rise and overflow the bordering plains. The best-known instance of such river flooding is supplied by the Nile, which makes possible the existence of millions of people on the Xile oasis in the broad .frican desert. The rising of the waters begins in June in the
