56 NUTEITIVE MATTER IS DISSOLVED. 



sential difference between natural digestion and the artificial imitation of 

 it, either as respects the order of action or the final result. Moreover, 

 the anatomical consideration that the food is yet outside the body, though 

 it is inside the stomach, should be sufficient to remove all errors of that 

 kind. A living surface, such as the skin, never exerts any chemical ac- 

 tion at a distance ; and the lining membrane of the stomach, both as re- 

 gards its physiological origin and its anatomical relation, is nothing more 

 than a reflected continuation of the skin. The act of digestion is com- 

 pleted long before the nutrient material is taken up by the lacteals and 

 veins, and thrown into the torrent of the circulation. But then, and not 

 till then, is the food fairly in the interior of the body. 



The lacteals and veins can not exert their absorbent action on a sub- 

 stance presented to them unless it is dissolved in water. If not abso- 

 lutely dissolved, at least it must be in that condition of minute subdivis- 

 ion which we see in emulsions. Though it has been stated that insolu- 

 ble substances, such as charcoal, can find their way into the circulation 

 in the solid state, there does not appear to be a sufficient weight of evi- 

 dence to support such an improbability. In the economy of plants, it is 

 In plants, all a general rule that nothing can have access to the interior of 

 nutrient mate- t} ie i r system except it be dissolved in water. All the vari- 



rial must be in ITT i 



solution in \va- ous gases and saline substances they require are obtained in 

 ter - a state of solution ; the former are introduced, for the most 



part, through the leaves, the latter through the roots. The object aimed 

 at in the construction of the digestive apparatus of the animal mechanism 

 is absolutely the same. Plants use as their food inorganic matter only ; 

 the chief materials on which they depend, such as the salts of ammonia 

 and carbonic acid, are abundantly soluble in water. The ascending sap 

 obtains the former from decaying organic residues in the ground ; the at- 

 mosphere presents the latter unceasingly to the leaves ; and since the 

 economy of many plants requires earthy salts, as silicates and phos- 

 phates, which are of sparing solubility in water, the difficulty arising from 

 that want of solubility is avoided by the introduction of an immense quan- 

 tity of water, which, after bringing into the plant the needful amount of 

 mineral material, is evaporated off at the leaves. But the food of animals 

 is essentially organic, and this, before it can be received into their blood, 

 must be brought into the dissolved state. It must be submitted to a pre- 

 paratory operation or series of operations. However complicated these 

 The operations or the niechanism which accomplishes them may be, the end 

 on the food are aimed at is clear. The action begins by the cutting, tearing, 



purely chemic- , 11-11 i j 



aland median- and crushing movements of the teeth, which break down all 

 ical> the larger portions, and carry on the process as far as it is 



possible by mechanical means. The stomach then continues the subdi- 

 vision by chemical agency, to the end that a condition of solution may be 



