226 DISEASES OF CATTLE, SHEEP, 00 ATS, ETC. 



selves satisfactory. There are so many conditions which enter into 

 the process of infection that no single classification will give a suf- 

 ficiently correct or comprehensive idea of it. These statements 

 will be easily understood if the different infectious diseases in the 

 following pages be studied with reference to the way or ways in 

 which each disease may be contracted. Enough has been said, there- 

 fore, to show that, if we wish to make ourselves acquainted with 

 the dangers of any given disease, we must study that disease and 

 not rely upon any single word to tell the whole story. 



Infectious diseases have, as a general rule, a period of incuba- 

 tion, which comprises the time elapsing between the exposure to the 

 infection and the actual appearance of the disease. This period 

 varies with the malady. The most common symptom of this class 

 of diseases is fever. The severity of the fever is measured by the 

 temperature of the animal and tnis is readily and accurately ascer- 

 tainable by the clinical thermometer. The other symptoms are 

 variable and depend upon the particular organ or organs most im- 

 plicated. Loss of appetite, cessation of rumination and milk secre- 

 tion, and general dullness are symptoms quite invariably present in 

 most infectious diseases. 



During the course of infectious diseases secondary diseases or 

 complications may arise which are largely due to bacteria other than 

 those producing the original malady. These complications are 

 often so severe as to become fatal. In general it may be stated 

 that they are due to filthy surroundings, and hence cleanliness may 

 become an important aid to recovery. 



The treatment of infectious diseases is given under each malady 

 so far as this is allowable or advisable. These diseases are not, as 

 a rule, amenable to treatment. When the symptoms have once ap- 

 peared the disease is apt to run its course in spite of treatment, 

 and, if it is one from which animals usually recover, all that can 

 be done is to put them into the most favorable surroundings. Many 

 infectious diseases lead sooner or later to death, and treatment is use- 

 less so far as the sick are concerned, and it may be worse than, 

 useless for those not yet infected. All animals suffering with in- 

 fectious diseases are a menace to all others more or less directly. 

 They represent for the time being manufactories of disease germs, 

 and they are giving them off more or less abundantly during the 

 period of disease. They may infect others directly or they may 

 scatter the virus about, and the surroundings may become a future 

 source of infection for healthy animals. This leads us to the sub- 

 ject of prevention as the most important of all which claim our at- 

 tention. In this place only a few general remarks will suffice to 

 bring the subject oefore the reader. 



The most important thing is to keep disease away from a herd 

 or farm. To do this all sick or suspicious animals should be avoided. 

 A grave form of disease may be introduced by apparently mild or 

 trivial cases brought in from without. It is generally conceded 

 that continual change and movement of animals are the most potent 

 means by which infectious diseases are disseminated. 



