513 



CELLULAR TISSUE. 



ducing any sufficient proof in corroboration of 

 their views, had recourse to an expedient but 

 too frequently adopted by physiologists when 

 the real nature of any vital process escapes their 

 detection. 



The only way in which the apparently con- 

 tradictory results of experiment and observation 

 can be reconciled, is by attending to a combina- 

 tion of vital and physical processes, that has 

 been too much neglected in investigating the 

 characters of living bodies ; that is to say, it 

 must be recollected that " life," to borrow the 

 philosophic expression of Dr. Arnott,* " is a 

 superstructure on physics and chemistry," and 

 that those phenomena which are essentially de- 

 pendent on the ordinary laws of matter are 

 controlled and modified by the superior prin- 

 ciple of life. In the case of the cellular sub- 

 stance this remark is peculiarly applicable ; and 

 from reflecting on all the facts relative to that 

 tissue both in a state of health and disease, 

 -I have arrived at the conclusion that the phe- 

 nomena of its contractile force are the com- 

 bined results of one of the common proper- 

 ties of matter, viz., elasticity; and of a vital 

 process, viz., nutrition. It is a well-known 

 fact that the existence of elasticity in any inor- 

 ganic substance requires a particular state or 

 arrangement of its particles, and that if the 

 necessary condition be but partly fulfilled, or 

 be entirely wanting, that property is only 

 slightly displayed, or is totally absent. The 

 same principle strictly applies to the living- 

 body; and in the cellular substance the required 

 condition is, a definite proportion between the 

 solid fibres and the interstitial fluids, which 

 state is maintained by the agents of the circu- 

 lation and secretion, namely, the bloodvessels 

 and lymphatics. Any thing which interferes 

 with this proportion, either the excess of Huids, 

 as in anasarca or phlegmonous erysipelas, or 

 the diminution of the humours, as in old age 

 and in many diseases, will impair or destroy the 

 phenomena observable in the sound state of the 

 cellular membrane, and will explain in the 

 former case, the pitting which is seen on making 

 pressure on the skin ; and in the latter, that 

 flabbiness and wrinkling of the integument 

 about the face and other parts of the body, so 

 characteristic of those advanced in life or re- 

 duced by disease. We can in this manner 

 understand how a class of phenomena may be 

 dependent on a physical property, and yet 

 be modified by the condition of the vital powers, 

 so as to become impaired by disease, and 

 destroyed by death. 



The exhalation and absorption of which the 

 cellular substance is the seat, have been sup- 

 posed by many high authorities to be effected 

 by its elastic contractility ; but it is probable 

 that these phenomena, although in part de- 

 pendent on that property, are principally pro- 

 duced by the power of imbibition, which, ac- 

 cording to the experiments of MM. Magendie 

 and Fodera, exists in all the soft parts of the 

 body. 



Functions. The offices accomplished by 



* Elem, of Physics, Introd. p. xxvi. 



this substance in the economy seem to be, first, 

 that of uniting together the various constituent 

 parts of the body, and of keeping them in situ 

 by its contractile force ; secondly, of facilitating 

 their movements by means of its lubricating 

 fluid, and thus preventing the injurious effects 

 of friction and concussion ; and lastly, of fur- 

 nishing an appropriate structure for their recep- 

 tion. It has also been supposed that, being a 

 bad conductor of caloric, it will tend to pre- 

 serve the uniform temperature of the body. 



Development. The first trace of an organized 

 substance observed in the embryo consists of a 

 very soft and pulpy cellular tissue, which at 

 this early period is loaded with fluid; and 

 being homogeneous in its nature, it presents 

 neither fibres nor interstices, although it may 

 be readily permeated by air or liquids, so as to 

 produce small cells, and may likewise be drawn 

 out into glutinous filaments. In proportion as 

 the several organs become developed, it acquires 

 greater consistency, and is at the same time 

 diminished in quantity. At the period of birth 

 it is still, however, in a very soft and imperfect 

 state, and only acquires its proper density by 

 slow degrees ; in old age, being deprived of a 

 large portion of its fluid, and perhaps otherwise 

 deteriorated, it loses much of its elastic force; 

 and this circumstance, joined to its diminished 

 bulk, is a principal cause of that loss of rotun- 

 dity so conspicuous in the bodies of aged 

 persons, and of the flabbiness of the several 

 organs. 



The power of reproduction is greater in this 

 than in any other tissue, so that it is not only 

 readily formed again within certain limits when 

 it has been destroyed, but it even appears to 

 supply the place of other and dissimilar struc- 

 tures which may have been lost by disease. 



The cellular substance presents but few mo- 

 difications of importance when examined in 

 the different classes of animals, except, indeed, 

 that it is generally believed to constitute the 

 entire body in those species that are placed at 

 the bottom of the scale. The Porifera afford an 

 example of the simplest form of the cellular tex- 

 ture with which we are at present acquainted ; 

 the body of these animals consists of a soft 

 gelatinous substance composed of translucent 

 globules, which, however, are not perceptibly 

 joined together ; so that there is in this instance 

 nothing of that fibrous structure, which is the 

 great characteristic of the cellular membrane in 

 the human body and in the higher orders of ani- 

 mals. In the semifluid and jelly-like body of the 

 Polypifera and of some of the Acalephce, there 

 is merely a pulpy substance, which, although it 

 may exhibit a distinct digestive cavity, and even 

 tubes communicating with this, yet no mus- 

 cular tissue has hitherto been discovered. In 

 these animals, however, rapid movements are 

 seen in the cilia ; and the tentacula, when pre- 

 sent, together with the entire body, are capable 

 of spontaneous motion; it is evident, then, in 

 these and other instances, that if, as is gene- 

 rally supposed, there be an absence of muscles, 

 the cellular tissue must be endowed with a pro- 

 perty totally wanting in that substance as it 

 exists in the higher animals. When it is con- 



