THE BLOOD. 



loss may be repaired by regeneration of a new portion of tissue of ths same 

 kind ; but the extent to which this restoration is possible is very different 

 in different textures. Thus, in muscle, a breach of continuity may be 

 repaired by a new growth of connective tissue ; but the lost muscular sub- 

 stance is not restored. Regeneration occurs in nerve ; in bone it takes 

 place readily and extensively, and still more so in fibrous, areolar, and 

 epithelial tissue. The special circumstances of the regenerative process in 

 each tissue will be considered hereafter ; but we may here state generally, 

 that, as far as is known, the reproduction of a texture is effected in the 

 same manner as its original formation. 



In experimental inquiries respecting regeneration, we must bear in mind, 

 that the extent to which reparation is possible, as well as the readiness with 

 which it occurs, is much greater in many of the lower animals than in man. 

 In newts, and some other cold-blooded vertebrata, indeed (not to mention 

 still more wonderful instances of regeneration in animals lower in the scale), 

 an entire organ, a limb, for example, is readily restored, complete in all its 

 parts, and perfect in all its tissues. 



In concluding what it has been deemed advisable in the foregoing pages to state 

 respecting the development of the textures, we may remark that, besides what 

 is due to its intrinsic importance, the study of this subject derives great interest 

 from the aid it promises to afford in its application to pathological inquiries. Re- 

 searches which have been made within the last few years, and which are still zealously 

 carried on, tend to show that the structures which constitute morbid growths are 

 formed by a process analogous to that by which the natural or sound tissues are 

 developed : some of these morbid productions, indeed, are in no way to be distin- 

 guished from areolar, fibrous, cartilaginous, and other natural structures, and have, 

 doubtless, a similar mode of origin ; others, again, as far as yet appears, are peculiar 

 in structure and composition, but still their production is with much probability to be 

 referred to the same general process. The prosecution of this subject, however, does 

 not fall within the scope of the present work. 



THE BLOOD. 



PHYSICAL AND ORGANIC CONSTITUTION. 



The most striking external character of the blood is its well-known colour, 

 which is florid red in the arteries, but of a dark purple or modena tint in the 

 veins. It is a somewhat clammy and consistent liquid, a little heavier than 

 water, its specific gravity being 1052 to 1057; it has a saltish taste, a 

 slight alkaline reaction, and a peculiar faint odour. 



To the naked eye the blood appears homogeneous ; but, when examined 

 with the microscope, either while within the minute vessels, or when spread 

 out into a thin layer upon a piece of glass, it is seen to consist of a trans- 

 parent colourless fluid, named the " lymph of the blood," " liquor sanguinis," 

 or " plasma," and minute solid particles or corpuscles immersed in it. 

 These corpuscles are of two kinds, the red and the colourless : the former 

 are by far the most abundant and have been long known as "the red 

 particles," or "globules," of the blood; the "colourless," "white," or 

 " pale corpuscles," on tha other hand, being fewer in number and less 

 conspicuous, were later in being generally recognised. When blood is 

 drawn from the vessels, the liquor sanguinis separates into two parts ; 

 into fibrin, which becomes solid, and a pale yellowish liquid named serum. 

 The fibrin in solidifying involves the corpuscles and forms a red consistent 



