134 



ANIMAL. 



In the tribes which have a circulation, in 

 the strict sense of that word, we find two or- 

 ders of vessels, arteries and veins, in which 

 the nutritive juices, or blood, moves respec- 

 tively in opposite directions, from the trunks 

 towards the branches in the one, from the 

 branches towards the trunks in the other. 

 These vessels anastomose freely by their ex- 

 tremities, which terminate and originate in 

 every part of the body, and, farther, meet in a 

 common central cavity, which, when furnished 

 with muscular parietes, is entitled heart. With- 

 in the circle of vessels thus established, the 

 nutrient fluid of animals is in perpetual or next 

 to perpetual motion during the term of their 

 lives. In the higher classes the main agent in 

 producing this motion is the central organ in 

 which the veins and arteries meet; but it is not 

 the only cause of the circulation, this act going 

 on vigorously in circles and in situations 

 wherein the heart's action can have very little 

 influence, and in some tribes where the heart 

 is even altogether wanting. 



The circulation in the greater number of 

 animals, however, is a more complicated pro- 

 cess than that which has just been described ; 

 it consists, in fact, of two parts perfectly dis- 

 tinct from each other; one whereby the blood 

 is exposed to the action of the air in the appa- 

 ratus which, in connexion with the respiratory 

 process, we have denominated lungs, gills, &c., 

 another by which it is finally distributed for 

 the uses of the system. This double circula- 

 tion is accomplished by a great variety of con- 

 trivances (vide articles HEART and CIRCULA- 

 TION). In some tribes we find more than one 

 vessel, two, or three, each apparently inde- 

 pendent of the other, though communicating 

 together, which are subservient to the distri- 

 bution of the nutrient fluid to the different parts 

 of the body of the animal. 



The chief differences between vegetables and 

 animals with respect to their circulation, con- 

 sequently, appear to be these : in vegetables 

 the motion of the sap or aliment takes place 

 through the whole of one of the tissues of 

 which they consist; that of the cambium or 

 proper nutritive fluid through the whole of 

 another of these tissues, in opposite directions 

 simply, and by the intermedium of fascicu- 

 lated, very numerous, and independent vessels ; 

 whereas the aliment of animals does not cir- 

 culate through their bodies, but the nutritive 

 fluid prepared from it is collected and con- 

 fined within peculiar channels, connected at 

 both extremities in such wise as to form a con- 

 tinuous circle. In vegetables we perceive 

 nothing like tendency towards or distribution 

 from a central reservoir, nothing like ramifica- 

 tion from larger to smaller branches, &c. ; con- 

 sequently not!) ing like a heart, as we do in 

 animals above the very lowest. In vegetables, 

 again, we see nothing like the two-fold distri- 

 bution of the nutrient fluid within different 

 orders of vessels, the one to the organs of 

 respiration, the other to the system at large, as 

 occurs among all animals possessing a some- 

 what complicated organization. 



We have recognized the heart as the princi- 



pal cause of the motions performed by the .fluids 

 within the bodies of animals ; but as neither 

 all animals have a heart and yet exhibit their 

 nutrient fluids in motion ; indeed, as a distinct 

 circulation of the blood may be demonstrated 

 in many animals, and probably takes place 

 in all at periods of their evolution anterior 

 to the existence of a heart ; and further, as 

 vegetables exhibit a motion or circulation of 

 their fluids without the agency of any special 

 organ, it is necessary to acknowledge a new 

 law by virtue of which the fluids of organized 

 beings generally go their round or reach their 

 destination. This law has been designated as 

 the propulsive, a power inherent in the nu- 

 tritive globules of living beings, and one of 

 the special laws superadded to the general and 

 all-pervading forces that regulate the universe. 

 One fundamental distinction between the 

 bodies of the organic and inorganic kingdoms 

 we have found based upon the permanence of 

 the parts, the constancy of the relations, affi- 

 nities, &c. of the component elements of the 

 one, and the incessant changes or renewals and 

 decompositions which these parts or elements 

 undergo in the other. The various processes 

 by which the aliment of vegetables and animals 

 is converted into a succus proprius, the final 

 means of their individual conservation and 

 evolution we have now examined ; we have 

 only farther to discover this nutrient juice con- 

 verted into the different tissues and substances 

 of which organized beings consist, to have a 

 complete view of the vital act of nutrition. 

 But here we are compelled to pause. Of the 

 processes by which this transformation is ac- 

 complished we know next to nothing ; all we 

 are assured of is, that each tissue and organ 

 seizes upon and converts into its proper sub- 

 stance those particles enveloped in the general 

 mass of circulating fluids brought into rela- 

 tionship with it, and which are adapted to this 

 purpose, at the same time that the particles 

 which have already been consolidated and 

 served their office are reduced to the fluid 

 state, absorbed back into the torrent of the 

 circulation, and afterwards either abstracted 

 and thrown out of the body by the operation 

 of certain organs charged with this duty, or 

 being subjected to the action of the atmos- 

 pheric air in the lungs, gills, skin, &c. are 

 restored to their fitness once more to enter as 

 temporary constituents of the organization. 

 It is evident, therefore, that we are only ac- 

 quainted with this operation in its effects. 

 The act of ultimate nutrition has been happily 

 entitled one of continuous generation in each 

 living being and its parts ; it takes place in 

 conformity with the laws of vitality instituted, 

 and probably originating and ending in living 

 organized beings. 



This subject, however interesting, we must 

 reluctantly forsake, referring to the article on 

 NUTRITION, and to the consideration of what 

 has been called the nisus formations, or plastic 

 power in our article on FCETAL DEVELOPMENT. 



Vegetables and animals, from this review, 

 appear to differ little from one another in all 



