302 OF THE PRIMARY TISSUES OF THE HUMAN BODY. 



noid cavity, apparently by the organization of a clot of blood that had been 

 effused in consequence of injury; and it exhibited a large varicose blood-channel, 

 which had no very definite wall, with a great number of smaller branching ves- 

 sels, having very distinct parietes. The blood of the large channel presented 

 blood-corpuscles of all dimensions, from the smallest appreciable size to that of 

 the fully -formed disk; those of the inferior or intermediate sizes being decidedly 

 more numerous than in ordinary blood. Combining these two facts, therefore, 

 the relatively low state of development of the largest channel, and the young 

 condition of the blood which it contained, there scarcely appears room for doubt 

 that the whole plexus was of independent origin, and was not derived from the 

 adjacent bloodvessels. On the other hand, it seems at least equally certain that 

 in the production of new parts for the repair of injuries, the tissue ordinarily 

 becomes supplied with bloodvessels, not by any such independent formation in 

 its own substance, but by mere out-growth from the capillaries of the subjacent 

 structure. "The vessel," according to the description of Mr. Paget, 1 " will first 

 present a slight dilatation in one, and coincidently, or shortly after, in another 

 point; as if its wall yielded a little near the edge or surface. The slight pouches 

 thus formed gradually extend, as fluid canals or diverticula, from the original 

 vessel; still directing their course towards the edge or surface of the new mate- 

 rial, and crowded with corpuscles, which are pushed into them from the main 

 stream. Still extending, they converge; they meet; the partition-wall, that is 

 at first formed by the meeting of their closed ends, clears away, and a perfect 

 arched tube is formed ; through which the blood, diverging from the main or 

 former stream, and then rejoining it, may be continuously propelled/ 7 Some- 

 times the projecting pouch in which the new vessel originates, gives way, and 

 the blood-corpuscles escape into the substance of the parenchyma ; at first they 

 lie there in a confused cluster; but before long they manifest a definite direction, 

 and the cluster bends towards the line in which the new vessel might have 

 formed, and thus opens into the other portion of the arch, or into some adjacent 

 vessel. 3 This formation of new passages in a determinate direction, by a pro- 

 cess of " channelling," indicates the existence of forces in the parenchyma 

 itself, that determine the direction in which the vessels shall prolong themselves, 

 when the new passage is formed by their outgrowth ; in fact, it would not seem 

 improbable that this outgrowth is itself but a sort of varicose dilatation, conse- 

 quent upon the breaking-down of the tissue into which it extends itself. And 

 it is conformable to this view, that, according to the observations of Mr. Travers, 3 

 when a new capillary arch is formed by outgrowth, it does not at once convey 

 a stream of blood; but isolated corpuscles enter it, and perform an oscillating 

 movement for some hours, before any series of them passes into it ; so that we 

 cannot regard the new canal as formed by the vis d tergo of the circulating 

 blood, as some have maintained it to be. 



296. The structure of the minutest Absorbent vessels is very similar to that 

 of the capillary Bloodvessels. Both in the substance of the tissues in which the 

 lymphatics take their origin, and in the extremities of the intestinal villi in which 

 are the radicles of the lacteals, they seem to originate in plexuses ; which, however, 

 are unlike those of the capillary bloodvessels, in communicating with trunks on 

 one side only. These plexuses are formed, according to the observations of Prof. 

 Kblliker (loc. cit.), on the same original plan with those of the bloodvessels; 

 namely, by the junction and fusion of processes from stellate cells, either with 

 each other, or with offshoots from previously-existing vessels. In the develop- 

 ment of the lymphatic tubuli, however, the union of the cells is in a more simple 



1 "Lectures on Repair and Reproduction," in "Med. Gaz." July 13, 1849, p. 



2 Paget, Op. cit., p. 72. 



8 "Physiology of Inflammation and the Healing Process," p. 77. 



71. 



