218 CONTAGIOUS DISEASES OF DOMESTICATED ANIMALS. 



(in any of the "N'orthern States) to become there acclimated, or, in other 

 words, have never passed a winter in the North. But the same cattle 

 iftakeu from their native range and tlriven or shipped south will grad- 

 ually lose their immunity in i>roportion to the distance they go further 

 south, and thus, if going far south, finally become liable to be infected 

 and to contract the fever. This shows the infectious principle must be the 

 more intense the further south the locality. 



2. If Texas or other Southern cattle, to all appearances themselves 

 perfectly healthy, are shipped or driven North, away from their native 

 range, after new grass has appeared and become interwoven or inter- 

 mixed with the old dead grass of last year's growth, which, owing to 

 the warmer weather and the usually abundant rains of the early South- 

 ern spring, is in a decaying condition, and these cattle, thus compelled 

 to eat both the intermingled old and new grass, have but once taken a 

 good meal of this mixed herbage, they will as soon as they arrive at a 

 certain latitude further north infect every trail and pasture on which 

 they graze, and every water-hole out of which they dnnk, with the in- 

 fectious principle of southern cattle fever. And the native Northern 

 cattle following them will, after some interval of time (period of incuba- 

 tion), contract the disease, as a rule, in its most fatal form. 



3. If Texas or other Southern cattle are moved to the North before- 

 any new grass has made its appearance on their nativ^e range, or rather 

 before the dead grass of last year's growth has commenced to decay, na 

 infection of Northern pasture, &c., will take place, no matter how far 

 north the Southern cattle may be shipped o'' driven. If, however, the 

 cattle, thus leaving their native range in the South earlj' in the season, 

 or in the winter, should travel slow enough to be yet within a part of 

 the South in which the southern cattle fever has its permanent source, 

 when warm weather and abundant spring rains cause a decay of the 

 old grass and start a vigorous growth of the new, the effect will be 

 precisely the same as if the cattle had been kept that long on their na- 

 tive range; only the infectious principle imparted to the Northern past- 

 ures, &c., may be a trifle less virulent, and taken up b}' Northern cat- 

 tle may cause a somewhat milder, though in a majority of cases yet 

 fatal, attack of the disease. I had repeated occasions to observe that 

 the fever, as a rule, is the mere severe the further south the source of 

 the infectious principle. 



4. Northern cattle shipped to Texas, or to other parts of the South^ 

 will contract the disease, and as a rule die of it, if only once pastured 

 soon after their arrival on land that contains both old and new grass — 

 particularly if it is so-called hog- wallow land — or if only once allowed to 

 drink out of a water-hole receiving the drainage of such land. 



5. Grown Northern cattle imported into Texas usually contract the 

 disease with more certainty, and in a more fatal form, than imported, 

 Northern calves and yearlings. Whether such is the case because the 

 latter have a smaller mouth, are more dainty eaters, and better able ta 



