ii) the Rearing and Feeding of Cattle. 
259 
breed. All these differences inust be due to some cause. I have 
ahead}' fully explained to you that the disappearance of food from 
the system is owing^ to a combustion of the food by means of the 
air inspired by the lungs. The oxygen which has once entered the 
system never again escapes from it without being united either 
with part of the body or of the food. 
Now, supjrose that we were feeding two pigs with precisely the 
same size of lungs, the same quantity of air is taken into their 
body at each respiration. If they received the same quantity of 
food, they must increase equally in size, because the same amount 
is expended by the air respired, and the remainder, being equal, 
must be assimilated. But let us give to one pig double the quan- 
tity of food that the other receives ; then, the air being only able to 
consume the same amount of food as before, the pig must increase 
twice as rapidly as the other. This is quite obvious. Again, 
suppose the pigs to have different sizes of lungs, — let us take the 
Berkshire and Neapolitan pigs, for example, and suppose the 
former to have larger lungs than the latter — let us assume in the 
proportion of two to one ; — if we give each of the pigs 30 lbs. of 
potatoes daily, the Neapolitan pig will, on the same quantity of 
food, increase twice as rapidly as the Berkshire, because, by our 
assumption, its lungs are only one half the size. This, in other 
words, means, that as only one half the quantity of oxygen enters 
its body at each respiration, this quantity can only consume half 
as much as the double quantity of air does in the Berkshire pig. 
That which is left in the body unconsumed must increase its size. 
A little consideration will show that the case cannot be otherwise. 
Now, to take a case without an assumption. The Leicester 
sheep have smaller lungs than the South Downs. In an experi- 
ment at Whitfield Example Farm it was found that a certain 
number of Leicesters, during a given time, reached 28 lbs. a 
quarter; while South Downs, with a greater consumption of food, 
reached in the same period only 18 lbs. a quarter.* As much 
more oxygen entered the bodies of the South Downs, a greater 
rjuantity of food was necessary to unite with it, and consequently 
their increase was slower. When an animal feeds slowly, or, in 
other words, when it possesses large lungs, we try to give it a 
greater aptitude to fatten, by crossing it with a breed which pos- 
sesses small lungs. Thus the Chinese pig we know to have small 
lungs, while those of the Irish pig are large. But a cross between 
these feeds more quickly than the Irish alone, because the Chi- 
nese pig has imparted to it its smallness of lungs. We know that 
the character of the lungs is generally handed down from parent 
to child. The hereditary tendency to consumption exhibited by 
* Inlbrmation furnished by the Earl ol Ducie. 
s 2 
