REPORT OF THE SECRETARY. 167 



stantly being received from the individual owners, as well as from 

 city and State officials. 



SCIENTiriC INVESTIGATIONS OF ANIMAL DISEASES. 



Scientific knowledge of the causes and nature of animal diseases 

 and their relation to human health is a necessary basis for adminis- 

 trative work in dealing effectively with such diseases. In the domain 

 of scientific research the Bureau of Animal Industry has had a large 

 share in the advancement of knowledge. The investigations of this 

 kind have been carried on by the Pathological, Biochemic, and 

 Zoological Divisions, and the Experiment Station. 



THE CATTJ-E TICK. 



Although some excellent results were obtained prior to 1897, the 

 energies of the scientific staff were centered upon the study of only a 

 few diseases. The country had but recently been freed from infec- 

 tious pleuropneumonia of cattle, and as Texas fever was apparently 

 the most serious animal disease existing at that time, much attention 

 was devoted to the study of its cause and prevention. The later 

 work relating to this disease has included the determination of the 

 shortest and longest periods of time in the development, at all stages, 

 in the life history of the Southern cattle tick, the carrier of Texas 

 fever of cattle; the determination that apparently healthy southern 

 cattle may continue to carry the parasite that causes Texas fever in 

 their blood for years after they have been removed from the so-called 

 infected territory and have been protected against all sources of infec- 

 tion, and the determination that noninfectious cattle ticks become 

 infectious and capable of causing Texas fever by living a single gen- 

 eration on the bodies of southern cattle that have been kept half a 

 dozen years or longer in apparently perfect health north of the Texas 

 fever territory, and away from all sources of infection. These re- 

 sults form a series of contributions of the greatest importance in the 

 practical work of the eradication of southern cattle ticks and the 

 prevention of Texas fever. 



The efficacy of arsenical dips as remedies for destroying cattle ticks 

 and the proper strengths of the dipping solutions have been proved 

 and determined by careful and prolonged investigations. Without an 

 efficacious remedy like the arsenical dip, progress in tick eradication 

 would be extremely difficult if not practically impossible. 



BLACKLEG VACCINE. 



The extensive losses of young cattle from blackleg, together with 

 the perfection of a protective vaccine by Kitt and other European 

 investigators, led to the inauguration in 1897 of the manufacture and 



