Part 100

Fig. 1. The cut surface of a healthy liver taken from a steer slaughtered for beef.

Fig. 2. The cut surface of the liver in Texas fever.

Fig. 3. Appearance of the urine in an acute, fatal case of Texas fever.

Fig. 4. Red corpuscles, magnified 1,000 diameters, containing the parasite of Texas fever. This appears as a blue point a near the edge of the corpuscle. The blood was taken from a skin incision. The case was nonfatal and occurred late in the fall.

Fig. 5. Red corpuscles from the blood of an acute, fatal case, 20 hours before death. The Texas-fever microbes a are shown as pear-shaped bodies, stained with methylene blue, within the red corpuscles. The larger body on the right b is a white blood corpuscle, also stained with methylene blue. (Magnified 1,000 diameters.)

PLATE XLVI. The cattle tick (Margaropus annulatus), the carrier of Texas fever.

Fig. 1. A series of ticks, natural size, from the smallest, just hatched from the egg, to the mature female, ready to drop off and lay eggs.

Fig. 2. Eggs, magnified 5 times.

Fig. 3. The young tick just hatched (magnified 40 times).

Fig. 4. The male after the last molt (magnified 10 times).

Fig. 5. The female after the last molt (magnified 10 times).

Fig. 6. A portion of the skin of the udder, showing the small ticks. From a fatal case of Texas fever produced by placing young ticks on the animal. (Natural size.)

Fig. 7. A portion of the ear of the same animal, showing same full-grown ticks ready to drop off. (Natural size.)

PLATE XLVII. The cattle tick (Margaropus annulatus).

Fig. 1. Dorsal view of male. (Greatly enlarged. Original.)

Fig. 2. Ventral view of male. (Greatly enlarged. Original.)

Fig. 3. Dorsal view of replete female. (Greatly enlarged. Original.)

Fig. 4. Ventral view of same.

PLATE XLVIII. Portion of a steer's hide, showing the Texas-fever tick (Margaropus annulatus). (Natural size. Original.)

PLATE XLIX. Fig. 1. Tick-infested steer.

Fig. 2. Dipping cattle to kill ticks.

PLATE L. Facsimile of poster used to show the difference between cattle of similar breeding raised on a tick-free farm in one case and on a ticky farm in the other.

* * * * *

CHRONIC BACTERIAL DYSENTERY.

Chronic bacterial dysentery is a chronic infectious disease of bovines caused by an acid-fast bacillus simulating the tubercle bacillus and characterized by marked diarrhea, anemia, and emaciation, terminating in death.

This disease was observed in the United States for the first time by Pearson in Pennsylvania cattle, and later by Mohler in Virginia cattle, and in an imported heifer from the island of Jersey at the Athenia quarantine station of the Bureau of Animal Industry.

Pearson proposed the name chronic bacterial dysentery for this affection, and it has also been termed Johne's disease, chronic bacterial enteritis, chronic hypertrophic enteritis, and chronic bovine pseudotuberculous enteritis by various European investigators. The disease was first studied in 1895 by Johne and Frothingham in Dresden, but they were inclined to attribute to the avian tubercle bacillus the cause of the peculiar lesions of enteritis which they observed. In 1904 Markus reported this disease in Holland, and subsequently it was observed in Belgium, Switzerland, Denmark, and Great Britain.

Cause.--The bacillus, which has been invariably demonstrated in the intestinal lesions and mesenteric lymph glands in this disease, is a rod about 2 to 3 microns long and 0.5 micron wide. It stains more or less irregularly, like the tubercle bacillus, and moreover the similarity goes further, in that the organism is also strongly acid-fast, which facts led Johne and Frothingham to surmise that the disease was caused by avian tubercle bacilli. However, it has now been plainly demonstrated that the bacillus of chronic bacterial dysentery is readily distinguished from the latter organisms, for while it resembles the tubercle bacillus in form and staining qualities, no one has succeeded in growing it in culture media or in reproducing the disease by injecting experiment animals.