512 CELLULAR TISSUE. 



ducing any sufficient proof in corroboration of this substance in the economy seem to be, first, 



their views, had recourse to an expedient but that of uniting together the various constituent 



too frequently adopted by physiologists when parts of the body, and of keeping them in situ 



the renl nature of any vital process escapes their by its contractile force ; secondly, of facilitating 



detection. their movements by means of its lubricating 



The only way in which the apparently con- fluid, and thus preventing the injurious effects 

 tradictory results of experiment and observation of friction arid concussion ; and lastly, of fur- 

 can be reconciled, is by attending to a combina- nishing an appropriate structure for their recep- 

 tion of vital and physical processes, that has tion. It has also been supposed that, being a 

 been too much neglected in investigating the bad conductor of caloric, it will tend to pre- 

 characters of living bodies ; that is to say, it serve the uniform temperature of the body, 

 must be recollected that "life," to borrow the Development, The first trace of an organized 

 philosophic expression of Dr. Arnott,* " is a substance observed in the embryo consists of a 

 superstructure on physics and chemistry," and very soft and pulpy cellular tissue, which at 

 that those phenomena which are essentially de- this early period is loaded with fluid ; and 

 pendent on the ordinary laws of matter are being homogeneous in its nature, it presents 

 controlled and modified by the superior prin- neither fibres nor interstices, although it may 

 ciple of life. In the case of the cellular sub- be readily permeated by air or liquids, so as to 

 stance this remark is peculiarly applicable ; and produce small cells, and may likewise be drawn 

 from reflecting on all the facts relative to that out into glutinous filaments. In proportion as 

 tissue both in a state of health and disease, the several organs become developed, it acquires 

 I have arrived at the conclusion that the phe- greater consistency, and is at the same time 

 nomena of its contractile force are the com- diminished in quantity. At the period of birth 

 bined results of one of the common proper- it is still, however, in a very soft and imperfect 

 ties of matter, viz., elasticity; and of a vital state, and only acquires its proper density by 

 process, viz., nutrition. It is a well-known slow degrees ; in old age, being deprived of a 

 fact that the existence of elasticity in any inor- large portion of its fluid, and perhaps otherwise 

 ganic substance requires a particular state or deteriorated, it loses much of its elastic force ; 

 arrangement of its particles, and that if the and this circumstance, joined to its diminished 

 necessary condition be but partly fulfilled, or bulk, is a principal cause of that loss of rotun- 

 be entirely wanting, that property is only dity so conspicuous in the bodies of aged 

 slightly displayed, or is totally absent. The persons, and of the flabbiness of the several 

 same principle strictly applies to the living organs. 



body; and in the cellular substance the required The power of reproduction is greater in this 



condition is, a definite proportion between the than in any other tissue, so that it is not only 



solid fibres and the interstitial fluids, which readily formed again within certain limits when 



state is maintained by the agents of the circu- it has been destroyed, but it even appears to 



lation and secretion, namely, the bloodvessels supply the place of other and dissimilar struc- 



and lymphatics. Any thing which interferes tures which may have been lost by disease, 



with this proportion, either the excess of fluids, The cellular substance presents but few mo- 



as in anasarca or phlegmonous erysipelas, or difications of importance when examined in 



the diminution of the humours, as in old age the different classes of animals, except, indeed, 



and in many diseases, will impair or destroy the that it is generally believed to constitute the 



phenomena observable in the sound state of the entire body in those species that are placed at 



cellular membrane, and will explain in the the bottom of the scale. The Porifera afford an 



former case, the pitting which is seen on making example of the simplest form of the cellular tex- 



pressure on the skin ; and in the latter, that ture with which we are at present acquainted ; 



flabbiness and wrinkling of the integument the body of these animals consists of a soft 



about the face and other parts of the body, so gelatinous substance composed of translucent 



characteristic of those advanced in life or re- globules, which, however, are not perceptibly 



duced by disease. We can in this manner joined together ; so that there is in this instance 



understand how a class of phenomena may be nothing of that fibrous structure, which is the 



dependent on a physical property, and yet great characteristic of the cellular membrane in 



be modified by the condition of the vital powers, the human body and in the higher orders of ani- 



so as to become impaired by disease, and mals. In the semifluid and jelly-like body of the 



destroyed by death. Polypifera and of some of the Acalephse, there 



The exhalation and absorption of which the is merely a pulpy substance, which, although it 

 cellular substance is the seat, have been sup- may exhibit a distinct digestive cavity, and even 

 posed by many high authorities to be effected tubes communicating with this, yet no mus- 

 by its elastic contractility; but it is probable cular tissue has hitherto been discovered. In 

 that these phenomena, although in part de- these animals, however, rapid movements are 

 pendent on that property, are principally pro- seen in the cilia; and the tentacula, when pre- 

 duced by the power of imbibition, which, ac- sent, together with the entire body, are capable 

 cording to the experiments of MM. Magendie of spontaneous motion; it is evident, then, in 

 and Fodera, exists in all the soft parts of the these and other instances, that if, as is gene- 

 body, rally supposed, there be an absence of muscles, 



Functions. The offices accomplished by the cellular tissue must be endowed with a pro- 

 perty totally wanting in that substance as it 



* Elem, of Physics, Introd. p. xxvi. exists in the higher animals. When it is con- 



