Mlcrohic Diseases Individually Considered. 335 



determine it is as yet incomplete ; some authors have 

 described a bacillus ; others, a bacillus and a coccus ; 



often showing irregular discolored patches beneath the capsule 

 which itself is non-adherent, points of extravasation in the pelvic 

 mucous membrane ; in many cases extensive effusion of bloody 

 serosity in the fat and connective tissue surrounding one or both 

 kidneys ; the urine contained in the bladder generally dark red 

 in color free from blood corpuscles but strongly albuminous, 

 sometimes of normal appearance ; congestion of the mucous folds 

 of the fourth stomach ; more or less hyper£emia and extravasation 

 in the walls of the small intestine have also been noticed. 



Etiology.— Te:s.as fever in its acute and best known form occurs 

 under two conditions, 1st, when northern cattle are shipped into 

 southern infected regions, and second, when cattle from perma- 

 nently infected regions, brought north during the summer months, 

 infect pastures in which susceptible cattle are subsequently al- 

 lowed to graze. In the first case the disease may, and frequently 

 does, appear two weeks after exposure to infection, in the second 

 a lapse of six weeks or more intervenes between the arrival of the 

 infection-bearing cattle and the outbreak of the disease. These 

 differences are attributable to the method by which the infec- 

 tion is conveyed into the bodies of susceptible animals. The in- 

 vestigations of Smith and Kilborne (afterward repeated with the 

 same results by others) have shown that this takes place through 

 the intermediation of cattie ticks {Boophilus bovis, Curtice), the 

 progeny of those adherent to the skin of the southern cattle. 

 The lapse of time between the arrival of these cattle and the out- 

 break of the disease represents the time required for the incuba- 

 tion of the next generation of these parasites along with the pe- 

 riod of incubation of the disease. In the case of cattle shipped 

 into permanently infected districts their invasion by ticks and 

 consequent infection may begin at once. It is possible also that in 

 permanently infected districts infection may occur by other means. 

 Later generations of ticks which come to development on sus- 

 ceptible cattle in the North are also capable of communicating 

 the disease. Horses, which may also be invaded by these para- 

 sites, do not obtain the disease, and the progeny of ticks which 

 have developed on these animals have not been shown to be dan- 

 gerous for cattle. 



Experimental inoculations.— TositWe results have been obtained 



