150 VEGETABLE SUBSTANCES. 



ness with wheaten bread. The following statement, 

 from Mr Jacob's Corn Tracts, contains, as it ap- 

 pears to us, all the facts that can be depended upon 

 for forming an opinion on this question : 



' If an acre of land, with the same degree of 

 labour bestowed upon it, and the same portion of 

 manure applied to it, yields 300 bushels of potatoes, 

 it may yield 24 bushels of wheat. The food pro- 

 duced by the former, at 38lbs to the bushel, will 

 then be ll,4001bs in weight; the food from the 

 latter, at GOlbs to the bushel, will be 1 ,4001bs, or 

 the weight of the wheat will be one-eighth that of 

 the potatoes. It is difficult to ascertain the quantity 

 of nutrition in a given quantity of either wheat or 

 potatoes. The chemical experiments of Sir Hum- 

 phrey Davy show that wheat contains about three 

 times the quantity of mucilage or starch, and of 

 gluten or albumen, of what is contained in a like 

 weight of potatoes ; but that potatoes contain also 

 about from three to four per cent of their weight 

 of saccharine matter, in which wheat is deficient, 

 though it abounds in barley. The difficulty of esti- 

 mating the nutritive power of the two substances is 

 not wholly removed by this appeal to chemistry, 

 because we are still ignorant of the effect which the 

 combination of the saccharine matter with the mu- 

 cilage and gluten may produce when used as ali- 

 ment. A small addition of the former to the two 

 latter may communicate to the whole mass a degree 

 of nutritive power very far exceeding its own sepa- 

 rate proportion of weight. Some inquiries have 

 been made as to the actual quantity of potatoes con- 

 sumed per head in families in Ireland, in Prussia, 

 and in Saxony ; but the answers varied to such a de- 

 gree, as to be little satisfactory. It does not appear 

 to me to be very far from the fact, if we estimate the 

 proportion of the nutritive power of wheat to that of 

 potatoes, as about seven is to two ; or that 21bs of 



