HEKEDITAEY DISEASES. 379 



with ointment of iodide of mercury. As soon as the animal 

 is considerably better, it should be sent to the butcher." 



Heeeditakt Diseases. — Mr. Finlay Dun, Lecturer on 

 Materia Medica and Dietetics at the Edinburgh Veterinary 

 College, after giving much attention to the subject of hered- 

 itary diseases in domestic animals, summed up his conclusions 

 as follows : 



1. "They are transmitted by the male as well as by the 

 female parent, and are doubly severe in the offspring of 

 parents, both of which are affected by them. 



2. They develop themselves not only in the immediate 

 progeny of one affected by them, but also in many subsequent 

 generations. 



3. They do not, however, always appear in each genera- 

 tion in the same form ; one disease is sometimes substituted 

 for another, analogous to it, and this again, after some 

 generations, becomes changed into that to which the breed 

 was originally liable, as phthisis (consumption) and dysentery. 

 Thus, a stock of cattle previously subject to phthisis, some- 

 times become affected for several generations with dysentery, 

 to the exclusion of phthisis, but by and by, dysentery disap- 

 pears to give place to phthisis. 



4. Hereditary diseases occur to a certain extent independ- 

 ently of external circumstances, appearing under all sorts of 

 management, and being little affected 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 devel- 

 oped 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. 



7. 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 wiU stiU remain and be greatly aggravated by 

 each attack. 



"In horses and neat cattle, hereditary diseases do not 



