No. 8. 



Scientific Agriculture. 



255 



tion; the inspirations and expirations are 

 the strokes of the pendulum which regulate 

 it. In our ordinary time-pieces, we know 

 with mathematical accuracy the effect pro- 

 duced on their rate of going, by changes in 

 the length of the pendulum, or in the exter- 

 nal temperature. Few, however, have a 

 clear conception of the influence of air and 

 temperature on the health of the human 

 body; and yet the research into the condi- 

 tions necessary to keep it in the normal 

 state, is not more difficult than in the case 

 of a clock.— Liebig's Letters. 



Scientific Agriculture. 



How many curious questions are suggested 

 by such observations as the following: Some 

 varieties of wheat are better suited for the 

 pastry-cook ; others, for the baker of bread. 

 Some samples of barley refuse to melt in the 

 hands of the brewer and distiller; and some 

 yield more brandy; while others lay on more 

 fat. The Scottish ploughman refuses bog 

 oats for his brose-meal, or for his oaten-cake, 

 because they make it tough; and the cot- 

 ter's family prefer Angus oats for their por- 

 ridge-meal, because they swell, and become 

 bulky and consistent in the pot, and go fur- 

 ther in feeding the children at the same cost. 

 The pea sometimes refuses to boil soft ; and 

 potatoes, on some soils and with some ma- 

 nures, persist in growing waxy. If Swedish 

 turnips sell for thirty shillings a ton — as in 

 large towns they often do — yellow turnips 

 will bring only about twenty-five, and white 

 globes, eighteen; while all the varieties 

 cease to feed well as soon as a second 

 growth commences. 



What is the cause of such differences as 

 these ] How do they arise ] Can they be 

 controlled ! Can we by cultivation remove 

 them! Can we raise produce of this or that 

 quality at our pleasure! 



Such questions, constantly arising, have 

 led to extended analyses of the food con- 

 sumed both by cattle and by man ; and from 

 these analyses — still far from being com- 

 plete — most curious, and most interesting, 

 and most practically important results have 

 already been obtained. Let us glance at 

 some of the partial generalizations which 

 have been arrived at, and which may be 

 provisionally adopted, by practical men. 



We have ^.Iready seen that all vegetable 

 productions contain from ninety to ninety- 

 eight per cent, of combustible or organic 

 matter. Now, this organic part has been 

 found, in all cases, to contain three different 

 classes of substances : ¥ 



First, the starch class, which compre 



hends starch, gum, and sugar, and certain 

 other substances of a similar kind. 



Second, the fatty class, which compre- 

 hends solid and liquid oils of various kinds, 

 of which the oils extracted from seeds and 

 nuts are familiar examples. 



Third, the gluten class, which compre- 

 hends the gluten* of wheat, vegetable albu- 

 men, vegetable casein, and some other anal- 

 ogous substances, the distinctive characters 

 of which have not as yet been thoroughly 

 investigated. 



These several classes of substances are 

 always to be found in sensible quantity in 

 all our cultivated crops; but their propor- 

 tions vary in different plants, in different 

 parts of the same plant, and in the same 

 part when the plants are grown in different 

 climates, on unlike soils, or by the aid of 

 different manures. Hence the occasional 

 differences in the sensible qualities of the 

 same vegetable, under different circum- 

 stances—the waxiness of the potatoe, the 

 hardness of the pea, and the stubbornness 

 of the barley— become intelligible. The 

 several organic constituents of the grain 

 and root crops are present in unlike propor- 

 tions, and necessarily give rise to unlike 

 qualities. 



But their unlike effects, in the feeding ot 

 animals, sug-gested a further train of inves- 

 tigation. The parts of animals are known 

 to" be differently built up, or with different 

 degrees of rapidity and success, by these 

 different varieties of vegetable produce ;— of 

 what, then, do the parts of animals them- 

 selves consist] The answer to this ques- 

 tion throws a new and beautiful light upon 

 our path, clearing up obscure points on the 

 way we have already trodden, and pointing 

 out new tracks, which it will prove interest- 

 in<T hereafter still further to explore. 



All animal substances— the flesh, bones, 

 and milk, of all living creatures— consist, 

 like the soil and the plant, of a combustible 

 and an incombustible part. In dry muscle 

 and blood, the incombustible or inorganic 

 part does not exceed two per cent., and in 

 milk evaporated to dryness, seven per cent. ; 

 while in dry bone it amounts to about sixty- 

 six per cent, of the whole weight. 



The combustible or organic part consists 



* When wheaten flour is made into a dough with 

 water, and this dough is washed with a stream of 

 water upon a sieve, as long as the water passes 

 through milky, a tenacious substance, like bird-lime, 

 remains behind. This is the gluten of wheat. Albu- 

 men is the name given by chemists to the white of the 

 egg ; and casein, that applied to the curd of milk. Of 

 both of these latter, an appreciable quantity is found 

 in almost every kind of vegetable food. 



