PATHOLOGY 



1235 



similar to S. icterohcemorrhagicB, and has named it Leptospira 

 icteroides. 



Pathology. — In yellow fever the cells of the liver swell, and, 

 pressing upon the bile capillaries, obstruct the flow of bile and 

 cause a hepatogenous jaundice, characterized by yellow staining 

 of the skin and tissues, and by the presence of bile in the urine. 

 Further, the swelling blocks the intralobular capillaries, causing 

 congestion of all the viscera drained by the portal vein, but especially 

 of the pyloric end of the stomach and the duodenum, because of 

 the arrangement of the veins from those parts. This stagnation 

 of the blood may allow a secondary bacterial infection to take 

 place, which shows its effect on the intestine and spleen. 



The liver cells degenerate so extensively in bad cases as to cause 

 the urea function to be considerably lessened in activity, and thereby 

 a condition of ammonisemia comes about, which produces most 

 serious toxic effects upon the brain and other organs. In addition, 

 the disease in some way seriously affects the endothelial lining of 

 the blood capillaries, producing haemorrhages in various parts of 

 the body. If these leading features of the pathology are borne in 

 mind, the post-mortem appearances and the symptomatology will 

 be easily understood. 



An attack generally confers a lasting immunity upon a person, 

 and second attacks afe rare, and it appears that the so-called 

 racial immunity of people living in endemic regions is really an 

 acquired immunity, due to mild attacks in childhood. Relative 

 immunity can be acquired by inoculation of infected blood heated 

 to 55° C. for five minutes. Further, it is found that the serum of 

 a convalescent has some protective power. 



The Blood. — ^There is no marked alteration in the numbers or 

 appearance of the erythrocytes, even in fatal cases. A few normo- 

 blasts are said to be present at times. On the other hand, there is a 

 decided loss of haemoglobin, though this is rarely much reduced in 

 the first three or four days; and haemoglobinsemia is said to occur 

 in fatal cases before death. But this does not appear to coincide 

 with the fall of specific gravity, which may be present without loss 

 of haemoglobin. 



The leucocytes do not appear to be distinctly increased in numbers, 

 varying from 3,200 to 20,000 per cubic millimetre, the increase, 

 when present, being largely caused by polymorphonuclear leuco- 

 cytes. The coagulation of the blood is diminished, and ammoni- 

 semia is thought to be present in bad cases. 



The Urine. — ^Albumen appears early — as a rule, on the second 

 day — and increases in quantity remarkably, especially in severe 

 cases. During convalescence it may disappear, or may last for 

 months. Bile is present about the fifth or sixth day, and red blood 

 cells may also occur, though leucocytes are rather rare. Casts are 

 present — ^first hyaline, then granular, and finally epithelial. Urea 

 is diminished in bad cases, and the diazo-reaction is believed to be 

 absent in uncomplicated cases. 



