PREFACE. IX 



prejudicial to fish, may have become mixed 

 with the water; and we ought to be able to 

 detect the cause at once, and with certainty. 

 We ought to know how such things are to be 

 prevented, and what the diseases of fish spring 

 from. But do we ? 



The agriculturist knows to a head or two 

 what amount of stock his farm will carry. He 

 knows "what kinds of roots are best suited, 

 not only for stock to feed on, but for his 

 various fields to grow. The cold land suits 

 one thing the dry land another. This will 

 grow swedes and that corn, this grass or what 

 not. He knows what species of food, and what 

 variety of it, will fatten his stock the quickest. 

 He knows what roots and cereals are the most 

 productive and pay best, and in what order they 

 should be planted. He knows what breeds of 

 stock suit his farm, and where to put them, and 

 when it is most profitable to him to get rid of 

 them. He would never think of putting a 

 Southdown sheep on a Highland sheepwalk, 

 nor a Welsh runt on a Hereford pasture, &c. 

 As a breeder and feeder, he knows how to cross- 

 breed and feed his stock, so as -even to change 



