418 BLOOD DISEASES, 



the falling of the temperature marking the cessation of the 

 destruction of the corpuscles, and the disappearance of the para- 

 site from the blood. The mortality varies greatly. A mid- 

 summer outbreak, when acute in its nature, is the most fatal, 

 and from this time there may be all gradations towards the mild, 

 non-fatal form of the disease. 



Etiology. — Several observers have reported the discovery of 

 various forms of bacteria in this disease. In 1883 Salmon 

 described a diplococcus obtained from spleen cultures. Detmers 

 found bacilli and micrococci in the liver, but none in the blood ; 

 and in 1888 Billings claimed the discovery of what he terms 

 the " true germ," an ovoid bacterium, staining at the ends, 

 similar to that of swine plague. All these contentions, however, 

 have now been apparently terminated by the discovery of a 

 parasite in the blood corpuscles, conveyed from Southern to 

 Northern cattle by cattle ticks (Boophilus hovis). At the experi- 

 mental station of the Bureau, near Washington, it was found by 

 experiments in 1889 that the disease can be produced by ticks 

 artificially hatched in the laboratory. 



The parasites thus conveyed are found in certain proportions 

 of the red corpuscles in the form of rounded or somewhat ovoid 

 or pyriform bodies, isolated or in pairs, in the acute form of the 

 disease, whilst in the mild form it appears that from 5 to 50 per 

 cent, of red corpuscles are found to contain coccus-like bodies, 

 sometimes on the border, and outside the corpuscles ; they are 

 from -nr^oT) to ToioX) of an inch in diameter, sometimes dividing 

 into two ; they, as well as the larger pyriform bodies seen in the 

 acute form, stain with aqueous solutions of aniline dyes, and 

 with hffimotoxylin. Both the large and small forms are con- 

 sidered to be different stages of the same parasitic protozoa 

 (Pi/osoma Mfjcminum, Dr. Theobald Smith). The smaller ones 

 are found in cattle exposed to the disease late in the season, or 

 during a second attack or relapse after passing through an acute 

 attack, and in milder cases during or previous to the season (hot) 

 of the acute disease. — (See Fig. 23.) 



Post-mortem Aiipearances. — Congestion of the vessels and 

 occasional patches of extravasation in the subcutaneous 

 tissues, blood sometimes thin and watery, lungs normal or 

 discoloured by congestive patches, heart congested ; petechial 

 spots on peri- and endocardium, spleen congested, its capsule 

 streaked from distension of its vessels. The wei^lit of the 



