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XIX. — Lecture on the Apjdications of Phyaiology to the Rearing 
and Feeding of Cattle. No. I. By Lyon Playfair, Ph. D., 
F.G.S., Honorary Member of the Royal Agricultural Society, 
&c. Delivered to the Society, December, 1842. 
1. On the General Principle. t of Nutrition and on the Food of 
Cattle. 
In compliance with the request of the Council of our Society, I 
have ventured to appear before you for the purpose of examining, 
in its scientific relations, one of the most important branches of 
Agricultural science. Recent discoveries have thrown much light 
upon the vital and chemical processes engaged in the nutrition of 
animals : it therefore became an important question, whether 
these discoveries tended to elucidate the practice of feeding 
cattle ? It would be presumptuous in any scientific man, how- 
ever exalted his rank in science, to endeavour to instruct an as- 
semblage such as this, or to recommend alterations in the practice 
of an art which he has learned in the closet and not in the field. 
But it may be permitted, even to the most humble cultivator of 
science, to examine the practice which you yourselves have per- 
fected, and to point out the laws of nature upon which that prac- 
tice depends. This is in accordance with the principles which 
your Society has adopted, and by which it has been induced to 
enrol amongst its members men professing the cultivation of 
various branches of philosophy. 
I iherefore thought it my duty, as a willing soldier of the So- 
ciety, to appear before you in obedience to the commands of our 
Council, and to endeavour, however humbly, to examine the sub- 
ject which it assigned. 
But before we can examine the applications of physiological 
science to the feeding of cattle, we must in the first place be pos- 
sessed of a clear conception of the leading theories connected with 
animal nutrition. The principal part of this lecture will be de- 
voted to this subject ; and in our next lecture we shall consider 
those theories in their more immediate applications to practice. 
Vegetables derive their principal nutriment from the air. Many 
mineralogists class air as a gaseous mineral. Hence the vegetable 
kingdom may be said to derive its nutriment from sources en- 
tirely inorganic. Animals, on the other hand, subsist only upon 
organic matter, i. e., upon substances which have at one time 
formed part of a living organised being. 
The primary nutriment of all animals consists of vegetable 
matter. The carnivora, indeed, live wholly upon flesh ; but the 
animals which furnished this flesh derived their nourishment from 
