398 MAINTENANCE OF ANIMALS. 



different animals ; they are necessarily smaller in amount among 

 those that are young and small, such as calves and sheep, than in 

 adult oxen and horses ; bi ; they do not occur the less on that ac- 

 count, and must, therefore, occasion errors of the same description. 

 What, then, shall we say ot' those small variations in the weig^ht in 

 a ewe or a ram, amounting perhaps to H or 2 lbs., ascertained in 

 the course of an experiment carried over two or three days, though 

 . conducted with the most scrupulous attention to accuracy in the 

 world 1 That they may very possibly have been purely accidental. 

 The first in every series of experiments on the maintenance of 

 animals, ought in fact to have it in view to ascertain the amount of 

 accidental variation in the weight of the creatures which are their 

 subjects ; as this variation is now on this side now Ou that, there is 

 an obvious advantage in having a certain number upon trial at a 

 time ; any error that occurs will thus be more apt to be corrected ; 

 afid the results may be held more worthy of confidence in propor- 

 tion as the numbers have been large from which they have been de- 

 duced Another cause of error, which I had occasion to discover 

 in the course of my experiments, appears to be connected with the 

 weight of the allowance. Equal in nutritious value, different allow- 

 ances may still have very different weights ; it is obvious, that a ra- 

 tion of hay and corn will weigh much less than its equivalent in 

 roots, tubers, or green meat. Animals that have been kept tor some 

 lime upon a dry diet, if put on one that is very bulky and watery, 

 will inmiediately increase very considerably in weight ; and their 

 increase is both so sudden and so great, that it is impossible to as- 

 cribe it to augmented nutrition, to tlesh and fat laid on. The ani- 

 mals are simply distended, their paunch and bowels are filled with a 

 larger quantity of food than they were before ; and the state of dis- 

 tension continues, though it suffers accidental variations, so long as 

 the new course of feeding is persisted in. In opposite circum- 

 stances, as when animals that have been long upon soft and watery 

 food, are suddenly put upon hard diet, they always drop very con- 

 siderably in weii^ht. These sudden changes throw disorder and 

 contradiction into the conclusions, and puz/lcd me greatly until I 

 discovered their cause. It is obvious that no kind of reliance can 

 be placed upon the conclusions which have been come to from single 

 weighings made at the end of each partii-ular course of alimentation, 

 'i'o get at results which shall be worthy of any credit, the animals 

 that are to be made the subjects of experiment nmst be tVd for sev- 

 eral days upon the particular ration that is to be approved, in order 

 to be brought to the state of body which may be said to belong in 

 particular to each system of dieting, before being weighed ; it is 

 only when this is attained, indeed, that the experiment can be held 

 to be properly begun ; and then it is to be continued for a sufhcient 

 length of time to lessen the influence of those accidental variations 

 of weight, of which I have spoken so particularly. It is perhaps 

 needless to observe, that any increase in weight and the maintenance 

 of that increase, are not always of themselves sufficient signs for 

 afhrming that tnc course then followed is superior or equal to the 



