1 FORMATION OF BLOOD-CORPUSCLES. 



decidedly and so generally as has been sometimes alleged; and this observation 

 accords with the statement of Mr. Hewson on the same point. 



Dr. Rees has examined the fluid contained in the thoracic duct of the human 

 subject. It was obtained from the body of a criminal an hour and a half after 

 execution, and, from the small quantity of food taken for some hours before death, 

 it must have consisted principally of lymph. It had a milky hue with a slight tinge 

 of buff; part of it coagulated feebly on cooling: its specific gravity was 1024. Its 

 analysis, compared with that of chyle from the ass, showed less water, more albumen, 

 less aqueous extractive, and a great deal less fat. 



FORMATION OF THE CORPUSCLES OF THE LYMPH AND CHYLE. 



The lymph-plasma appears to consist fundamentally of blood-plasma, which, 

 having exuded from the capillary blood-vessels and yielded nutritive material to the 

 tissues, is, with more or less admixture of waste products, returned by the lymphatics. 

 As to the origin of the lymph and chyle corpuscles, it may, in the first place, be 

 observed that the greatly increased proportion of these bodies in the vessels which 

 issue from the lymphatic glands, and the vast store of corpuscles having the same 

 characters contained in the interior recesses of these glands, are unmistakeable indi- 

 cations that the glands are at least a principal seat of their production. They are, 

 most probably, produced by division of parent corpuscles or cells contained in the 

 glands, and in some measure also by further division of corpuscles thus produced, 

 after they have made their way into the lymphatic vessels. The corpuscles found 

 sparingly both in chyle and lymph before passing the mesenteric glands may be in 

 part formed in the agminated and solitary follicular glands of the intestine which, 

 though differing" much in form, yet in essential structure have much in common 

 with the lymphatic glands and may come partly also from the irregular deposits of 

 pale corpuscles, which have recently been recognised in the intestinal mucous mem- 

 brane. Lymph-corpuscles are supposed also to be produced in the spleen, and in the 

 thymus and thyroid glands; but corpuscles, although few in number, and not 

 invariably present, have been found in the lymph of various regions of the body 

 before it has reached the glands, and they are present in the lymph of cold-blooded 

 vertebrata, whose lymphatic vessels, although forming a well developed system, do 

 not pass through glands. It, therefore, seems necessary to admit some further source 

 of the corpuscles ; but what this may be is very much a matter of conjecture. It 

 has been suggested that lymph-corpuscles are produced by multiplication of cells in 

 the epithelium which lines the lymphatic vessels, in the same way as mucus-cor- 

 puscles are supposed to be formed from the epithelium of mucous membranes. 



FORMATION OF THE BLOOD-CORPUSCLES. 



In the embryo ofbatracliians. In the early embryo of the frog and newt (in which, 

 perhaps, the steps of the process are best ascertained), at the time when the circu- 

 lation of the blood commences, the corpuscles in that fluid appear as rounded cells, 

 filled with granular matter, and of larger average size than the future blood-corpuscles. 

 The bodies in question, although spoken of as cells and presenting a regularly defined 

 outline, have no separable envelope. They contain, concealed in the midst of the 

 granular mass, a pellucid globular nucleus, which usually presents one or two small 

 clear specks, situated eccentrically. The granular contents consist partly of fine 

 molecules, exhibiting the usual molecular movements ; and partly of little angular 

 plates, or tablets, of a solid substance, probably of a fatty nature. After a few days, 

 most of the cells have assumed an oval figure, and are somewhat reduced in size ; 

 and the granular matter is greatly diminished in quantity, so that the nucleus is 

 conspicuous. Now, also, the blood-corpuscles, previously colourless, have acquired a 

 yellowish or faintly red colour. In a further stage, the already oval cell is flattened, 

 the granules entirely disappear, the colour is more decided, and, in short, the blood- 

 corpuscle acquires its permanent characters. From this description it will be seen 

 that the blood-cells which first appear agree in nature with the embryonic cells 

 (described at page xvi), and ^they are, in all probability, produced by the process of 

 segmentation, which is known to take place in the frog's ovum. The different parts 

 of the embryo in its early condition, the heart, for example, are for a time, entirely 

 composed of cells of the same kind, and all have probably a common origin. 



