FUNCTIONAL VARIATION 97 



overfed, but whether the same individual would make cheaper 

 returns on less feed is not so well known as it should be. In 

 the mechanical world the highest return of energy per unit of 

 consumption is realized when the machine is working full but 

 somewhat below its maximum capacity. Doubtless the same 

 principle holds with living machines, but on this point we are 

 sadly in need of accurate information. 



On one point we are certain. The animal (or the plant) is able 

 to adjust itself to a wide range of food supply, providing the 

 change be gradually made. Not only individuals but whole fam- 

 ilies for generations live in a condition of semi-starvation, often 

 quite ignorant of their real condition, if indeed they are not so 

 indifferent as to prefer to continue in the old way rather than to 

 disturb their tranquillity by increased exertion. Such a state 

 may easily become chronic in man or animal, but it is unprofit- 

 able because all other functions are suspended or reduced to a 

 minimum in order that the vital functions may be discharged at 

 all and the animal not die outright. There is no nicer problem 

 for the stockman and the feeder than this : How much shall I 

 put into this animal machine in order to realize the highest net 

 efficiency, after first providing for those activities which are 

 necessary to the life of the machine, the vital functions ? 



Influence of hard conditions. Under hard conditions the func- 

 tions of life may be disturbed but not destroyed. Under these 

 conditions valuable activities are carried forward upon a reduced 

 scale, and they often give rise to losses that are no less serious 

 because invisible. The most common example of this is in the 

 case of ill-fed or much-abused animals and of badly nourished 

 crops or trees : some milk is secreted, but it is insufficient and 

 its quality is poor ; the plant is weak, with little resisting power 

 against insects or disease, and with little ability to mature its 

 crop ; the apples are there, but they suffer for the means of 

 development. 



Every one who has had experience with unthrifty animals or 

 plants knows how difficult and how slow is the process of resto- 

 ration of normal activity after it has once been seriously checked 

 by neglect or disease. This is because the condition readily 

 becomes constitutional, tending to continue through life. 



