63 BOARD OF AGRICULTURE. 



4. Ilereditary diseases occur to a certain extent independently 

 of external circumstances ; appeai'ing under all sorts of manage- 

 ment, and being little afiected by changes of locality, separation 

 from diseased stock, or such causes as modify the production of 

 non-hereditary diseases. 



5. They are, however, most certainly and speedily developed in 

 circumstances inimical to general good health, and often occur at 

 certain, so called, critical periods of life, when unusual demands on 

 the vital powers take place. 



6. They show a striking tendency to modify and absorb into 

 themselves all extraneous diseases ; for example, in an animal of 

 consumptive constitution, pneumonia" seldom runs its ordinary 

 course, and when arrested, often passes into consumption. 



t. Hereditary diseases are less effectually treated by ordinary 

 remedies than other diseases. Thus, although an attack of phthisis, 

 rheumatism or opthalmia may be subdued, and the patient put out 

 of pain and danger, the tendency to the disease will still remain 

 and be greatly aggravated by each attack. 



In horses and neat cattle, hereditary diseases do not usually show 

 themselves at birth, and sometimes the tendency remains latent for 

 many years, perhaps through one or two generations and afterwards 

 breaks out with all its former severity." 



The diseases which are found to be hereditary in horses are 

 scrofula, rheumatism, rickets, chronic cough, roaring, ophthalmia 

 or inflammation of the eye, — grease or scratches, bone spavin, curb, 

 &c. Indeed, Youatt says, " there is scared}^ a malady to which 

 the horse is subject, that is not hereditary. Contracted feet, curb, 

 spavin, roaring, thick wind, blindness, notoriously descend from 

 the sire or dam to the foal." 



The diseases which are found hereditary in neat cattle are, 

 scrofula, consumption, dysentery, diarrhea, rheumatism and ma- 

 lignant tumors. Facts also render it probable that the recently 

 imported lung murrain, called pleuro pneumonia, is also of this 

 character. Neat cattle beijig less exposed to the exciting causes 

 of disease, and less liable to be overtasked or T^xposed to violent 

 changes of temperature, or otherwise put in jeopardy, their diseases 

 are not so numerous, and what they have are less violent than in 

 the horse, and generally of a chronic character. 



Scrofula is not uncommon among sheep, and it presents itself 

 in various forms. Sometimes it is connected with consumption ; 

 sometimes it aiTccts the viscera of the abdomen, and particularly 



