292 Dr. Play fair on Agricultural Experiments. [May 30, 



practical result of importance would have been arrived at ; but 

 they have laid down as an agricultural dogma, that " nitrogen is 

 the manure for wheat, and phosphorus and sulphates for turnip," 

 thus re-introducing the notion of specifics into the laws of manure. 

 "What, in the present stage of physiology, would be thought of a 

 similar dogma in regard to animals? Because a horse contains 

 more muscle, though less fat than a cow, it would not be permitted 

 as a law of nutrition, to say that " Carbon is the food for a cow, 

 and nitrogen for a horse ;" or because the sinewy Arab contains 

 less bone earth than the large-boned Highlander, " Nitrogen is the 

 food for an Arab, and phosphorus for a Highlander." 



This introduction of the idea of specifics into agriculture is 

 dropping the veil of Isis over the whole subject. The sum of 

 nutrition is made up of two factors, air food and earth food. Both 

 factors are of equal importance. To discuss whether air food or 

 earth food does most for particular crops is like discussing which 

 side of a pair of scissors is most useful in cutting, or whether the 

 upper or lower jaw is of most use in chewing. Dr. Playfair 

 discussed at length the conditions of durable fertility of a soil, 

 showing that the earth food was the capital of the farmer, and that 

 any diminution in his capital should only be made by a deliberate 

 and intelligent decision. For example, on a limestone soil it would 

 be legitimate to draw upon lime without replacement, or in heavy 

 clay soils upon alkalies. But as no soil is equally rich in all ingre- 

 dients, an unintelligent draught on the soil will soon destroy it, for 

 when one ingredient of earth food becomes in mbiimo the fertility 

 is reduced to its proportion, and is destroyed when it is used up. 



Dr. Playfair then proceeded to show how the chief recent 

 experiments in manures, which were rendered graphically in dia- 

 grams, bore out these views. Among others a series of experiments 

 made in Saxony to show the duration of the action of manures led 

 to conclusive results. Thus, in one case, an addition of 11 lbs. 

 of phosphoric acid produced an augmentation of a half more crop 

 of clover containing 158 lbs. more of earth food and nitrogfen, thus 

 showing, not that phosphoric acid was a specific, but that it was the 

 body in minimo, and this being supplied, the crop was enabled to 

 thrive and appropriate from the air and the soil the large quantities 

 of other ingredients necessary for its development, but which were 

 of no use when one ingredient was deficient in its necessary pro- 

 portional quantity. 



All the variations of district or local agriculture, instead of 

 representing specifics, which varying in them, would by contradictory 

 experience destroy one another, represent only immediate require- 

 ments of particular soils having different bodies in minimo. 



The only " specific " that should be admitted into farming is a 

 knowledge of the laws upon which nutrition depends. As long as 

 farming is carried on without an ac(iuaintance with these laws 

 on the part of its cultivators, great progress cannot be expected, 



