34 
THE CULTIVATOR. 
required. The plant compounds and prepares the mate¬ 
rials of the muscles—the stomach only picks out the 
bricks, as it were, from the other building materials, and 
sends them forward to be placed where they happen to 
be wanted.” (p. 589.) 
Here we find the author of these lectures agreeing 
with Dumas and Boussingault in a work recently pub¬ 
lished in this country by the title of “ The Balance of Or¬ 
ganic Nature,”—but these opinions were also entertained 
by Liebig. 
The animal frame receives a portion of its substance 
from the atmosphere, and expels carbon from the lungs. 
On the subject of respiration Johncton observes (p. 594) 
as follows: 
“ But for what purpose essential to life do animals re¬ 
spire? If the starch and sugar (as previously stated) be 
so necessary to feed the respiration—the breathing itself 
must be of vital importance to the living animal. 
(e Some doubts still exist upon this point. It is gene¬ 
rally believed, however, that carbon is consumed or giv¬ 
en off from the lungs for the purpose of sustaining the 
heat of the living body. When starch, or sugar, or gum, 
are burned in the open air, they are changed into car¬ 
bonic acid and water, and at the same time produce much 
heat. It is supposed that in the body the same change— 
the conversion of starch and sugar into carbonic acid and 
water—taking place, heat must in like manner be pro¬ 
duced. A slow combustion, in short, is supposed to be 
going on in the interior of the animal—the heat of the 
body being greater, in proportion to the quantity of car¬ 
bonic acid given off from the lungs. In favor of this 
view many strong reasons have been advanced, but there 
are also objections against it of considerable weight 
which cannot as yet be satisfactorily removed.” 
(C Were we to adopt this opinion in regard to the main 
purposes served by respiration as the true one, it would 
afford a very distinct reason for the large amount of starch 
existing in all our cultivated crops. Respiration, accor¬ 
ding to this view, is necessary to supply heat to the ani¬ 
mal, and this respiration is most simply and easily fed by 
the starch contained in the vegetable food. The life and 
labors of the plant again minister to the life and labors 
of the animal.” 
That animal heat was derived from respiration was 
long since pointed out by Lavoisier in France, and Priest¬ 
ley in England, but they were not so certain as to the 
manner of its production. 
se By the separation of carbonic acid (says our author, 
p. 596, note) which may be given off by the lungs—of 
water, which may or may not remain in the system— 
and of a portion of oxygen which may be used up in va¬ 
rious ways in the blood, the starch or sugar of the food 
may be converted into fat. 
t{ That in some such way these substances may be 
changed into the fat of animals, was first insisted upon and 
explained by Liebig, and it is probable, as I have said in 
the text, that in cases of emergency fat is really formed 
in the animal body from such kinds of food. But when 
Liebig put forth his views on this subject, it was not 
known that vegetable substances naturally contained so 
large a proportion of fat as has since been found in them. 
The necessity for the constant production or formation 
of fat in the body itself, therefore, is not now so appa¬ 
rent, and the soundest opinion, according to our present 
knowledge, seems to be that, while the vegetable food 
usually supplies all the fat ready formed which the ani¬ 
mal requires, yet that a conversion of a certain part of 
the starch, gum, sugar, and even of the cellular fibre 
of the food, into fat, may take place, when all the wants 
of the body are not supplied by the fat which the food 
naturally contains. Of course this opinion applies only 
to animals in perfect health. In certain diseased states 
of the body a larger and more constant production of fat 
from the food may take place, as appears to be the case 
in animals which no diminution of food seems to pre¬ 
vent from laying on fat.” 
In the seventh section of the 21st lecture (p. 500) 
Johnston affirms that the health of the animal can be sus¬ 
tained only by a mixed food. From this summary we 
may learn a valuable lesson in dispensing food to ani¬ 
mals, and the Graham philosophers may read a lesson 
that will teach them how to live. 
“ From what I have already stated, you see that the 
vegetable food eaten by a full grown animal for the pur¬ 
pose of keeping up its condition, should contain: 
“ 1st. Starch or sugar , to supply the carbon given off in 
respiration. 
“ 2d. Fat or fatty oil, to supply the fatty matter which 
exists more or less abundantly in the bodies of all ani¬ 
mals. 
“ 3d. Gluten and fibrin, to make up for the natural 
waste of the muscles and cartilage. 
“ 4th. Earthy phosphates, to supply what is removed 
from the bones of the full grown animal by the daily 
waste, and— 
ee 5th. Saline substances^-sulphates and chlorides—to 
replace what is daily rejected in the excretions. 
“ Hence the food upon which any animal can be fed 
with the hope of maintaining it in a healthy state must 
be a mixed food. Starch or sugar alone, or pure fibrin 
or gelatine alone, will not sustain the animal body, be¬ 
cause these substances do not contain what is necessary 
to build up all its parts, or to supply what is daily given 
off during respiration and in the excretions. The skillful 
feeder, therefore, will not attempt to maintain his stock 
on any kind of food which does not contain a sufficient 
supply of every one of the kinds of matter which the bo¬ 
dy requires.” 
There is much in these three lectures to interest the 
scholar, the man of leisure, or even the laborious farmer, 
who may read, and read again, and advantageously ap¬ 
propriate the information therein contained, as well as in 
the preceding parts before published. We will conclude 
our remarks on Johnston by giving his concluding sum¬ 
mary, which, to those who have not read his work, will 
explain its nature and contents. 
“ § 18. Concluding section.” (p. 519.) 
“ I have now brought the subject of these lectures to a 
close. I have gone over the whole ground which in the 
outset I proposed to tread. It is the first time, I believe, 
that much of it has been trodden by scientific men, and 
I have endeavored in every part of our journey to lay be¬ 
fore you, as clearly as I could, every thing we knew of 
the country we passed over, in so far as it had a practical 
bearing, or was likely to be susceptible hereafter of a 
practical application. 
“ In the first Part, I directed your attention to the or¬ 
ganic portion of plants—showed you of what substances 
it consisted—on what kind of organic food plants live— 
and by what chemical changes the peculiar organic com¬ 
pounds of which they consist, are formed out of the or¬ 
ganic food on which they live. 
“ In the second Part, I explained in a similar way, the 
nature, composition, and origin of the inorganic portion 
of plants. I dwelt also, upon the nature, origin and na¬ 
tural differences which exist among the soils on which 
our crops are grown, and from which the inorganic con¬ 
stituents of plants are altogether derived. This led me 
to explain the connection which exists between agricul¬ 
ture and geology, and the kind of light which this inte¬ 
resting science is fitted to throw upon the means of prac¬ 
tically improving.the soil. 
“ In the third Part, I dwelt upon the various means 
which may be adopted for increasing the general pro¬ 
ductiveness of the land—whether these means be of a 
mechanical or chemical nature. The whole doctrine of 
manures was here discussed, and many suggestions offer¬ 
ed to your notice, which have already led to interesting 
practical results. 
« In the fourth Part, I have explained the chemical 
composition of the several kinds of vegetable produce 
which are usually raised for food—showed upon what 
constituents their nutritive values depend—and how soil, 
climate and manure, affect their composition and their 
value as food. The nature and composition of milk and 
its products, butter and cheese—the theory of their ma¬ 
nufacture, and the circumstances upon which their res¬ 
pective quantities and qualities depend—and lastly the 
way in which food acts upon and supports the animal bo¬ 
dy, and how the value of the manures they make is de¬ 
pendent upon the purpose for which the animal is fed— 
