FORMATION OF CELLS. 421 



searches of Barry, Schwann, and Valentin, that the whole structure originates 

 in a single cell ; that this cell gives birth to others analogous to itself, and these 

 again to many future generations ; and that all the varied tissues of the Animal 

 body are developed from these, although no difference can be, in the first 

 instance, observed among them. The multiplication of cells appears to take 

 place upon the plan just stated, two or more being produced within the parent 

 vesicle ; and this alike in the earliest condition of the embryo, and in the more 

 advanced stages of the formation of its tissues. (See Plate I., Figs. 9 12, 

 and Explanation.) The organizable fluid, then, prepared by the digestive 

 process, is converted into organized tissue, by supplying the materials for this 

 continual reproduction; the formation itself is dependent upon the powers of 

 the solid texture. 



560. This is not, however, the only mode in which new cells are produced 

 in the Animal body ; for they may originate in Fibrin, from nuclei or cyto- 

 blasts, which are formed by the aggregation of minute granules ; just as do 

 those of the Plant in the organizable gummy fluid of the ovule. Both require 

 for their perfect performance, that the fluid should be in contact with a living 

 tissue ; and, when this condition is supplied, there seems to be no necessity 

 for any further assistance ; but traces of cellular organization may often be 

 discovered in Fibrin, even after it has been drawn from the vessels of the 

 living body, though more frequently, perhaps, in that which has coagulated 

 within the vessels after death.* The cells, where they present themselves, 

 possess nuclei, and have all the characters of being in progress of development ; 

 and frequently the nuclei can be distinguished when no cells yet appear. 

 It is, however, when Fibrin is effused, in the form of Coagulable Lymph, on a 

 cut surface, or on an inflamed membrane, that this process of organization most 

 unequivocally displays itself. Soon after the coagulation, a number of granular 

 bodies may be seen in the mass ; and these soon present appearances which 

 indicate that they serve as nuclei for the formation of cells. In this condition 

 they are known as Exudation-Corpuscles. The layers of these soon acquire 

 such a consistence, that they may be peeled off in cohering shreds from the 

 membranes to which they are attached ; and the cells when first formed present 

 a ruddy yellow colour, which corresponds with that of the Chyle-globules. 

 The Exudation-Cells are laid flat over one another, forming many super- 

 imposed layers, which unite into membranous expansions, bearing a strong 

 resemblance to the layers of flat cells of which Epithelium is composed ; their 

 margins are at first rounded, and they are united by a connecting medium, 

 which gradually disappears, leaving the sides coherent to each other, so that 

 the figure of the disk is changed into a polygon. These cells afterwards give 

 place to the various forms of tissue that are to present themselves in the new 

 fabric, by a series of changes which will be hereafter more fully described. 

 If the general principle be correct, that no Cell can be produced, save from a 

 germ prepared by a pre-existing cell, it is obvious that such germs must be 

 contained in the Liquor Sanguinis, and must escape from the blood-vessels 

 which pour it forth. When their extreme minuteness is considered, this may 

 not be deemed improbable. The formation of similar cells in the Clot of Blood 

 drawn directly from the vessels, and even in that which has coagulated within 

 them, seems to add weight to this idea. We have reason to believe that such 

 granules are being continually set free by the rupture of the White Corpus- 

 cles of the Blood ( 577) ; and reasons will hereafter be given for the belief, 

 that they may be the germs of the Epithelial Cells, to which the layers o 

 Exudation Cells bear so strong a resemblance. It is well known, that 

 character of organisms of a low grade is very much influenced by the circum- 



* See Mr. Gulliver's Appendix to Gerber's General Anatomy, p. 31. 

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