452 YELLOW FEVER 



which have occurred in the mucous and submucous coats. The 

 intestine may be normal, but is often congested and may be 

 ulcerated ; the mesenteric glands are enlarged. The liver is in 

 a state of fatty degeneration of greater or less degree, but often 

 resembling the condition found in phosphorus poisoning. The 

 kidneys are in a state of intense glomerulo-nephritis, with fatty 

 degeneration of the epithelium. There is congestion of the 

 meninges, especially in the lumbar region, and haemorrhages 

 may occur. The other organs do not show much change, 

 though small haemorrhages under the skin and into all the 

 tissues of the body are not infrequent. In the blood a feature 

 is the excess of urea present, amounting, it may be, to nearly 

 4 per cent. 



Etiology of Yellow Fever. Although a large amount of 

 bacteriological work has been done on yellow fever, this has 

 now chiefly a historical interest, as it is now known that the 

 causal agent is not one of the ordinary bacteria, but belongs to 

 the group of ultra-microscopic organisms. 1 A mosquito acts as 

 the intermediate host, and the facts detailed below point to the 

 organism passing through some cycle of development in the 

 body of the insect. The analogy of malaria makes it extremely 

 probable that the organism is a protozoon, but as this has not 

 yet been completely proved we have not felt justified in altering 

 the position of the disease and placing it amongst the protozoal 

 infections. As bacteriological work led up to the establishment 

 of our knowledge regarding the nature of the disease, some 

 reference must be made to it. 



A very full research into the bacteriology of yellow fever 

 was that of Sternberg,- the result of which was that of the 

 varied organisms isolated, one which he called the bacillus x 

 appeared possibly to have some relationship to the disease. 

 Sanarelli in 1897 obtained cultures of an organism which he 

 called bacillus icteroides, and which he considered to be the 

 cause of yellow fever ; it is probably identical with the bacillus 

 x of Sternberg. Subsequent observations made by others 

 gave conflicting results, some finding this bacillus, others 

 failing to do so. The bacillus icteroides, as described by 

 Sanarelli, belongs to the paratyphoid group, possessing lateral 

 flagella, growing on gelatin without liquefaction, and fermenting 

 glucose but not lactose. Reed and Carroll found that it was 

 practically identical with the bacillus of swine cholera. It 



1 In several diseases the existence of such causal factors is suspected. 

 Other examples are foot and mouth disease, South African horse-sickness, and 

 the contagious pleuro-pneumonia of cattle. 



