This disease is also due to the action of a specific microbe (see p. 353), and is characterized by a lesion in the intestine. The morbid poison finds entrance by the intestine, and produces irritation of the follicles and in its further passage of the mesenteric glands.

The Affection in the intestine consists of an inflammatory swelling of the closed follicles and of the mucous membrane in their neighbour hood, the inflammation often going on to necrosis and sloughing. The disease has usually its point of greatest intensity at the lower extremity of the ileum, and it is often possible to see various stages of the process in proceeding from above downwards through the small intestine till it culminates close to the ileo-caecal valve.

In the normal state, especially in the adult, the Peyer's patches and the solitary follicles are very slightly prominent. The patch viewed from the surface shows a congeries of shallow depressions separated by slightly elevated ridges, which run in from the general mucous membrane, and form a kind of network. It is in the depressions that the follicles are placed. In typhoid fever there is at first a general swelling of the patch; it is an inflammatory swelling accompanied by abundant infiltration of leucocytes which occupy both the closed follicles and the mucous membrane. The patch is obviously raised and its margins somewhat abrupt (Fig. 397, a). Viewed from the surface there is at this early stage simply an exaggeration of the normal appearance. The ridges of mucous membrane are swelled so that the depressions are more hidden, and an appearance is produced which has been compared to that of the convolutions of the brain in miniature. The swollen patch has a pinkish or whitish colour. At the same time the solitary follicles show themselves as elevations at intervals.

As the time goes on the whole tissue gets more and more infiltrated with leucocytes (Fig. 398), and the raised patch gets more solid and its surface more homogeneous. The invasion of round cells extends to the submucous and muscular coats, even to the serous, and passes to some extent beyond the patch. A similar condition occurs in the solitary follicles; they also present a marked increase in size, and are less defined, by reason of the infiltration around them.

On this condition follows Necrosis (Fig. 397, b). The infiltrated and altered patch or solitary follicles forms a slough, of larger or smaller size. This slough remains adherent for a time, and like all sloughs in the intestine it becomes brown or yellow from the biliary colouring matter, which stains dead tissue, while the living structures are able to resist it. Generally there is a single slough on a Peyer's patch, not involving the whole patch, but of considerable superficial extent (see figure). Sometimes there are several sloughs corresponding to some of the closed follicles of which the patch is made up.

Diagrammatic representation of Peyer's patches in typhoid.

Fig. 397. - Diagrammatic representation of Peyer's patches in typhoid (ever, a, early stage with swelling of the patch; b, later stage with sloughing; c, ulcer with infiltrated walls.

(THIERFELDER).

Portion of a Peyer's patch in an early period of typhoid fever.

Fig. 398. - Portion of a Peyer's patch in an early period of typhoid fever, a, mucous membrane which becomes raised when the swollen patch is reached; b, internal layer, and c, external layer of muscular coat; d, swollen patch composed of round cells with dilated blood-vessels. At the right of the section the round cells are invading the submucous tissue and approaching the muscular coat, x 16.

After a time the slough separates and an Ulcer is left with infiltrated base and margins (Fig. 397, c). The ulcers are confined to the patches and solitary follicles, so that they repeat their shape and locality. The walls are succulent and vascular, and considerable haemorrhage may occur from them. The ulceration may extend more deeply than the mucous membrane, involving a necrosis of the muscular and even of the serous coat, so that Perforation may result. Perforation may occur in one of two ways. In the first place an ulcer may extend in depth till it penetrates through the muscular and serous coats. In this case the process is somewhat gradual, and there is generally an inflammation of the peritoneum sufficient to cause adhesion and prevent the intestinal contents passing into the abdominal cavity. In the second place, perforation sometimes occurs in a manner comparable to the perforation of the pleura in phthisis pulmonalis which leads to pneumothorax. The serous coat is undermined by the ulcer, and as its nutrition is cut off it undergoes necrosis. In such cases the brown slough may be visible on viewing the intestine externally. A partial separation of the slough may allow of perforation, and as this form is more acute and not so likely to be accompanied by considerable adhesions, the contents of the intestine are more apt to escape into the peritoneal cavity and produce fatal peritonitis.

When Recovery takes place from the fever, the process in the intestine retrogrades. According to the stage reached will be the exact process of resolution. If, in any part, ulceration has not yet occurred, then there is a gradual diminution of the patch and a return to the normal. If ulceration exists the ulcer fills up and cicatrizes. The Cicatrix, however, remains long, often with a slaty colour, but not unusually with much puckering. It may indeed be a flat cicatrix in which the intestinal wall is merely thin and transparent. This is shown in Fig. 399, which represents the conditions in the ease of a girl who died of pneumonia a year after having passed through an attack of typhoid fever.

The Lymphatic glands of the mesentery enlarge, and present on section a red injected appearance and soft consistence. There may be necrosis here also, giving rise to an opaque greyish condition in the midst of the gland. When recovery takes place the glands return to the normal, and the sloughs are usually absorbed, although they may become caseous and subsequently calcareous.

It is to be remembered also that the Spleen is enlarged, and there is here more than in typhus fever a swelling of the Malpighian follicles, which are lymphatic in structure, and so the spleen is firmer and paler on section than normal (see p. 524). The specific microbe tt also present in the spleen.