OBJECT OF EXPERIMENTS IN PHYSIOLOGY. 57 



sugar in water, and, at last, nothing remains except 

 the gluten, in the form of a spongy mass, the minute 

 pores of which can be seen only by a microscope. 



Chemistry offers innumerable resources of this kind 

 which are of the greatest use in an inquiry into the 

 nature of the organs of plants ; but they are not used, 

 because the need of them is not felt. The most im- 

 portant organs of animals and their functions are 

 known, although they may not be visible to the 

 naked eye. But in vegetable physiology, a leaf is in 

 every case regarded merely as a leaf, notwithstand- 

 ing that leaves generating oil of turpentine or oil of 

 lemons must possess a different nature from those 

 in which oxalic acid is formed. Vitality, in its pe- 

 culiar operations, makes use of a special apparatus 

 for each function of an organ. A rose-twig engraft- 

 ed upon a lemon-tree does not bring forth lemons, 

 but roses. Vegetable physiologists in the study of 

 their science have not directed their attention to that 

 part of it which is most worthy of investigation. 



The second cause of the incredulity with which 

 physiologists view the theory of the nutrition of 

 plants by the carbonic acid of the atmosphere is, 

 that the art of experimenting is not known in physi- 

 ology, it being an art which can be learned accurate- 

 ly only in the chemical laboratory. Nature speaks 

 to us in a peculiar language, in the language of phe- 

 nomena ; she answers at all times the questions which 

 are put to her ; and such questions are experiments. 

 An experiment is the expression of a thought : we 

 are near the truth when the phenomenon elicited by 

 the experiment corresponds to the thought ; while 



burst, and allow the escape of the liquid. This liquid is the dextrine 

 of Biot, so called because it possesses the property of turning the plane 

 of the polarization of light to the right hand. It is white, insipid, trans- 

 parent in thin flakes and gummy. At 280° F. it becomes brown and 

 acquires the flavor of toasted bread. It is much employed by the French 

 pastry cooks and confectioners ; being reduced to powder it may be in- 

 troduced into all kinds of pastries, bread, chocolate, &c. For its prep- 

 aration, &c., see Ure's Dictionary of Arts and Manufactures ^oxidi. Web- 

 ster's Chemistry^ 510. 



