Yellow fever is an acute, infectious disease characterised by a sharp febrile paroxysm, gastric haemorrhage, jaundice and suppression of urine. The nature of the symptoms is exceedingly acute and intense. In those patients who die very soon after the invasion of the disease no definite lesions are found. In other cases hyperaemia and visceral degenerations are noted. These important changes are found in the liver and gastro-intestinal mucous membrane, and during the active progress of the infection digestion becomes almost impossible. The liver presents the lesions of parenchymatous hepatitis. The hepatic cells here and there are filled with granular material and oil globules. Many of them are distended or fused and have indistinct or absent nuclei. The small bile ducts are filled with degenerated epithelium, and the functional activity of the liver is therefore almost completely suspended. The whole alimentary canal presents the picture of acute catarrh, but the stomach particularly is softened, swollen, and ecchymotic, and it may be eroded.

The disease presents three different stages, the dietetic treatment of each of which is important, and it will therefore be necessary to briefly describe them. These stages are:

1. The cold period, followed by febrile reaction.

2. Remission or "stage of calm".

3. Second exacerbation, a uraemic condition or else collapse. The first stage begins with almost immediate vomiting and great prostration. The ejecta consist first of mucus, then bile in increasing amount, and finally, if the retching continues and muscular straining is severe, the irritability of the stomach in this period becomes greater than in almost any other disease. The slightest pressure over the epigastrium excites projectile vomiting. Constipation is present from the inability to retain fluids; the mouth becomes dry and the gums sore and swollen, and thirst is extreme. The urine is much diminished in volume as the changes in the liver progress, and the bile ducts are blocked with degenerated epithelium; the bile enters the blood, and the skin and conjunctivae become decidedly jaundiced.

After several days - usually four or five - these symptoms subside and the second period is reached. The duration of this period seldom exceeds two days, and it may continue but a few hours. It is a condition of calm, in which all symptoms are abated; the fever, which may previously have existed, subsides and the gastric irritation is lessened.

The third period promptly succeeds the second, and in it the symptoms of the first period return with renewed severity, and in addition a condition of uraemia develops. Haemorrhage of the stomach, known as " black vomit," is present in about one third of the fatal cases. The vomited material ejected during the course of the disease consists, first, of whatever food the stomach may contain, then of bile-tinged mucus, and finally of a deep brown or black acid semifluid substance resembling coffee grounds, which consists of red blood-corpuscles, pigment granules, degenerated mucus, epithelial cells, leucocytes, fatty matter, and serous fluid. The action of the gastric juice upon the extravasated blood pigment turns it dark brown or black. The quantity of this fluid may reach several pints. It is acrid and irritating to the fauces and mouth. The blood from the passively congested surface oozes freely from the capillary walls of the gastric mucous membrane. The intestinal mucous membrane may be similarly affected, in which case the stools are black and diarrhoeal. The urine becomes very scanty, and may be entirely suppressed.

There is haematuria.

Should recovery result, the jaundice continues for some days, but the other symptoms subside gradually and convalescence is always slow and may be retarded by various complications, among the most serious of which are an exceedingly irritable stomach and intestine. Errors in diet have been known to cause fatal haemorrhage from the stomach as long as a fortnight or three weeks after beginning convalescence. The heart action after such a severe ordeal is always feeble, and reparative and nutritive processes advance slowly. Irritability of the stomach may even persist for several months after the subsidence of all other symptoms. This brief account of the more important features of the disease emphasises the necessity for most careful dietetic management.