IMPROVING QUALITIES 499 



long legs, and large joints. No amount of feeding later in life 

 will make up for poor development. For this reason a mother 

 who is nursing needs more lime than she does at other times ; 

 and the same is true of a milk-producing cow. The hen that is 

 to lay eggs must also have a different diet from a hen that is 

 merely to remain alive or get fat. Other factors that influence 

 human life are important in maintaining the health of our stock 

 —temperature, exercise, exposure to wet or chilling, exposure 

 to infection, and injury by parasites. It is because the care 

 bestowed upon animals does make a difference that it is impor- 

 tant to know the biology of domestic animals. 



6. Getting better types of organisms. From time to time 

 there is introduced from a foreign country a variety of plant or 

 animal that is superior in some respects to any previously cul- 

 tivated in a given region. In this way the cultivators become 

 acquainted with better varieties of wheat, melons, beans, and 

 strawberries or sheep, swine, cows, and chickens. A transported 

 variety sometimes does better than the native because in the 

 new surroundings it does not have to contend with its usual 

 enemies. The agents of the Department of Agriculture are 

 constantly exploring the markets and foreign countries for 

 plants and animals that would suit special conditions in the 

 various parts of our country. 



From time to time there appears a freak plant or animal 

 among those in cultivation. Thus, there appeared among a flock 

 of sheep on a Massachusetts farm a male with very short legs and 

 very long trunk (see Fig. 212). This freak was not particularly 

 handsome, but when it had grown up the owner concluded that 

 this odd shape was of value, since it prevented the animal from 

 jumping fences. By using this as one of the parents for another 

 flock he obtained in the course of years an increasing number 

 of these short-legged sheep. At other times there have appeared 

 sheep with unusually long wool, and these were saved as a basis 

 for further breeding ; or sheep without horns arise suddenly in 

 a flock. These sports, as the breeders call them, or jumps, also 

 occur in plants. A wild dewberry without thorns was the basis 



