FUNCTIONS OF VEGETATIVE LIFE. 79 



it can absorb for itself that which is required, and it can readily part with that 

 of which it is desirable to get rid. Hence in such, no general circulation is 

 necessary. In Man, on the other hand, the digestive cavity occupies so small 

 a portion of the body, that the organs at a distance from it have no other 

 means, than their vascular communication affords, of participating in the 

 results of its operations ; and it is, moreover, necessary, that they should be 

 continually furnished with the organizable materials, of which the occasional 

 operation of the digestive process would otherwise afford only an intermitting 

 supply. This is especially the case, as already mentioned, with the nervous 

 system, which is so predominant a feature in the constitution of Man ; and we 

 accordingly find both objects provided for, in the formation of a large quantity 

 of a semi-organized product, which contains within itself the materials of all 

 the tissues, and is constantly being carried into relation with them. Blood 

 has been not unaptly termed chair coulante, or liquid flesh ; and although it 

 has been heretofore much questioned, whether it could be regarded as either 

 organized or endowed with vital properties, there now appears to be sufficient 

 reason for admitting that this is the case to a very considerable extent. The 

 propulsion of the blood through the large trunks, which subsequently divide 

 into capillary vessels, is due to the contractions of a hollow muscular organ, 

 the Heart ; but these, like the peristaltic movements of the alimentary canal, 

 are quite independent of (though frequently influenced by) the agency of the 

 nervous system ; and are therefore to be referred to the class of organic move^ 

 ments, such as occur in Vegetables. 



88. Upon the circulation of the blood through all parts of the fabric, depends 

 in the first place the Nutrition of the tissues. Upon this subject, formerly 

 involved in the greatest obscurity, much light has recently been thrown. In 

 the lowest classes of Plants and Animals, the whole or the greatest part of the 

 fabric is composed of vesicles or cells aggregated together, each of which has 

 a certain degree of independent vitality, and can live to a great extent by itself 

 alone, if duly supplied with nutriment. These cells differ but little from each 

 other in structure and endowment ; and the whole mass approaches far more 

 nearly, therefore, to the homogeneous character of inorganic bodies than does 

 the fabric of beings more elevated in the scale. This is precisely the condi- 

 tion of the embryonic structure of the highest Animals, at an early period of 

 their existence. Now in such fabrics, there is no distinct vascular system. 

 Every cell absorbs, either from the surrounding nutritious materials with 

 which it may be itself in contact, or from other cells in nearer proximity to 

 these, the aliment it requires for its own growth and reproduction ; and per- 

 forms all its vital processes, with little direct influence from any general con- 

 trolling power. The extension of the individual structure is partly effected by 

 the enlargement of its original vesicles ; but principally by the generation of 

 new ones within these ; and the latter, in their turn, go through the same pro- 

 cesses. In the higher Plants, however, we find a greater variety of tissues ; 

 but these all take their origin in cells. The straight tubes, for instance, which 

 convey the sap from the roots to the leaves, were evidently at first a line of 

 large cells, laid end to end, the partitions between which have broken down, 

 so that their cavities coalesce ; and the network of anastomozing vessels, by 

 which the descending or nutritious sap is conveyed through the tissues, may 

 be traced to a corresponding origin. The circulation of the sap which thus 

 regularly takes place, causes these Plants to receive the name of Vascular, 

 whilst the others are designated as Cellular ; but still it is to be remembered, 

 that the great bulk of the structure in the former, like the whole of the latter, 

 is composed of cellular tissue ; and that the central part of the islands, so to 

 speak, which are composed of this, in the interstices of the vascular network, 

 cannot be nourished in any other way than by absorption from the cells which 



