PERIPATETIC PHILOSOPHY 



PERITONEUM 



55 



Peripatetic Philosophy, a designation of 

 the philosophy of Aristotle (q.v.) and of his fol- 

 lowers*. It is of doubtful origin, being supposed to 

 have been derived either from his custom of occa- 

 sionally walking about (peripatein) during the 

 delivery of his lectures, or from the place in which 

 they were delivered being a shaded walk. 



Peripatlis, a genus occupying a unique posi- 

 tion between niyriopods and insects on the one 

 hand and annelids on the other. For, along with 

 the trachea; or air-tubes characteristic of insects, 

 Peripatus has the nephridia or excretory tubes 

 characteristic of the higher worms. The body 

 measures about two inches in length, is shaped like 

 that of a worm or caterpillar, but without external 

 rings, bears numerous ( 14 to 42 ) imperfectly -jointed 

 stump-like clawed feet, and has a soft skin, with 

 little of that chitin which is abundant as a cuti- 

 cular product in other arthropods. The head bears 

 a pair of mobile antenna;, a pair of mandibles in 

 the mouth, and a pair of oral papilla; from which 

 slime oozes. With this Peripatus catches its prey 

 of small insects, &c. The species live in moist 

 places under stones and bark, and are nocturnal in 

 their habits. Professor Sedgwick says that ' the 

 exquisite sensitiveness and constantly changing 

 form of the antenna-, the well-rounded plump body, 

 the eyes set like small diamonds on the side of the 

 head, the delicate feet, and, above all, the rich 

 colouring and velvety texture of the skin all com- 

 bine to give these animals an aspect of quite 

 exceptional beauty.' There are many remarkable 

 structural features : thus, the ventral nerves are 

 widely separate; the eyes are simple, like those 

 of an annelid ; the body-cavity is divided into 

 three longitudinal compartments, from which the 

 cavities of the legs are furthermore distinct. The 

 aexes are separate. The development varies con- 

 -i<l"rably in different species, for the ova may 

 ontain a considerable amount of yolk or none 

 at all. In several it has been olwerved that the 

 ells of the embryo are for a prolonged i>eriod 

 indistinctly separate from one another. The em- 

 bryos develop within the body of the mother- 

 animals ; when born they resemble the parents 

 except in size. The distribution is very wide ; in 

 South Africa there ore four species e.g. P. <<// n- 

 I', luilfmiri ; in New Zealand, P. nova; Zea- 

 liiiiiliir ; in Queensland, P. letickartii ; in Caracas, 

 /'. f.dwardsii ; and others from Demerara, Trinidad, 

 St Vincent, Chili. Quito, txc. The distribution, the 

 structure, and the development of Peripatus all 

 suggest that it is the survivor of an archaic type. 

 The genus is usually dignified as a special class 

 of Arthropods Prototracheata. See figure under 

 CATERPILLAR ; and monograph by A. Sedgwick, 

 <Juart. Journ. Micr. Sci., xxviii. (1888). 



Perissodactyla. See ARTIODACTYLA. 



Peristaltic Motion, the action of the mus- 

 cular coat of the intestines, by which the sub- 

 stances contained within it are regularly moved 

 onward. See DIGESTION. 



Peritoneum (Gr. periteinein, 'to extend 

 round'), a serous membrane, and, like all mem- 

 branes of this class, a shut sac, which, however, 

 in the female is not completely closed, as the 

 Fallopian tulws communicate with it by their free 

 extremities. The peritoneum more or less com- 

 pletely invests all the viscera lying in the abdom- 

 inal and pelvic cavities, and is then reflected upon 

 tin- walls of the abdomen, so that there is a visceral 

 and a parietal layer. Numerous folds are formed 

 by tin- visceral layer as i( passes from one organ to 

 another. They serve to hold the parts in position, 

 and at the same time enclose vessels ana nerves. 

 Soini! of these folds are termed Ligaments, from 

 their serving to support the organs. Thus, we have 



ligaments of the liver, spleen, bladder, and uterus 

 formed by peritoneal folds. Others are termed 

 Mesenteries (from the Gr. meson, ' the middle,' and 

 entet-on, 'the intestine '), and connect the intestines 

 with the vertebral column. They are the Mesen- 

 tery proper, the ascending transverse, and descend- 

 ing meso-colon, and the meso-rectum. Lastly, there 

 are folds called Omenta, whicli proceed from one 

 viscus to another. The great omentum always 

 contains some adipose tissue, which in persons 

 inclined to corpulency often accumulates to an 

 enormous extent. Its use appears to be ( 1 ) to 

 protect the intestines from cold by covering them 

 anteriorly as with an apron, and (2) to facilitate 

 their movement upon each other during their ver- 

 micular action. 



DISEASES OF THE PERITONEUM. The peri- 

 toneuni often becomes the seat of dropsical effusion, 

 lx>th in cases of general dropsy and in cirrhosis 

 of the liver. It may also be attacked by cancer, 

 either primary or secondary, and, like' all the 

 serous membranes, readily takes on inflammation 

 from various exciting causes. This inflammation 

 is termed Peritonitis, and may be either an acute 

 or a chronic disease. 



Acute Peritonitis, inflammation of the coating 

 of the bowels, but often popularly spoken of as 

 ' inflammation of the bowels,' generally presents 

 well-marked symptoms. It sometimes commences 

 with a chill, but severe pain in the abdomen is 

 usually the first symptom. The pain is at first 

 sometimes confined to particular spots (usually 

 in the lower part of the abdomen), but it soon 

 extends over the whole abdominal region. It 

 is increased, on pressure, to such an extent that 

 the patient cannot even bear the weight of the 

 bedclothes ; and to avoid, as far as possible, 

 internal pressure upon the peritoneum, he lies 

 perfectly still, on his back, with the legs drawn 

 up, and breathes by means of the ribs, in con- 

 sequence of the pain occasioned by the descent 

 of the diaphragm in inspiration. The breathing is 

 naturally shallow in these cases, and, less air being 

 admitted at each movement of respiration, the 

 number of those movements is increased. There 

 are perhaps forty or even sixty respirations executed 

 in a minute, instead of eighteen or twenty. The 

 pulse is usually very frequent, often 120 or more 

 in the minute, and small and tense, though occa- 

 sionally strong and full at the commencement of 

 the attack ; the temperature is usually raised, and 

 vomiting is almost always an early symptom. 

 After the disease has continued for a certain time 

 the belly becomes tense and swollen ; the enlarge- 

 ment being caused at first by flatus, and afterwards 

 also by the effusion of fluid, as may be ascertained 

 by percussion and palpation. The progress of the 

 disease is in general rapid. In fatal cases death 

 usually takes place within a week, and often 

 sooner. The symptoms indicating that the disease 

 is advancing towards a fatal termination are great 

 distention of the abdomen, a very frequent and 

 feeble pulse, a pinched and extremely anxious 

 appearance of the face, and cold sweats. 



Peritonitis rarely arises from exposure to cold 

 alone. It is frequently the result of local violence, 

 and of wounds penetrating the peritoneal sac, 

 including various surgical operations. In the 

 majority of cases it is due to extension of some 

 Inflammatory process in one of the abdominal 

 viscera, particularly the hollow viscera (stomach, 

 intestines, gall-bladder, urinary-bladder, womb). 

 It is sometimes caused by Bright's disease. Two 

 varieties call for special mention : puerperal peri- 

 tonitis, due to extension of septic inflammation of 

 ;he lining membrane of the womb after child-birth 

 or miscarriage, a most fatal form of disease ; and 

 peritonitis from perforation of one of the hollow 



