BLOOD. 



[ 86 ] 



BLOOD. 



Development of the Coloured Corpuscles. — 

 In the Vertebrata, two sets of coloured cor- 

 puscles are developed. The first, or embry- 

 onic blood-corpuscles, exist alone, until lymph 

 and chyle begin to be formed, when they are 

 gradually superseded by the second. 



The first blood-corpuscles are formed 

 from colourless nucleated cells, with 

 granular contents, identical with the 

 formative cells of the embryo, by their 

 losing the granules and becoming filled 

 with hsematine. These coloured, nucleated, 

 primary blood -cells, which are spherical, 

 larger and more deeply coloured than the 

 coloured blood-corpuscles of the adult, form, 

 with the colourless formative cells, the only 

 elements of the blood. Soon, however, many 

 of them begin to increase by division (PI. 40. 

 fig. 36), becoming elliptical and flattened, 

 and closely resembling the colom^ed corpus- 

 cles of Reptiles, producing two, rarely three 

 or four roundish nuclei, and then becoming 

 resolved into two, three or four new cells by 

 the formation of one or more annular con- 

 strictions. These corpuscles then gradually 

 lose their nuclei, become flattened and exca- 

 vated laterally, and form perfect coloured 

 corpuscles. 



The formation of the second set, or those 

 produced after birth and in adults, is more 

 obscure. The most probable view appears 

 to be that they are produced from the smaller 

 chyle-corpuscles, by their losing then nuclei, 

 becoming flattened, and producing hsema- 

 tine. At all events, corpuscles apparently 

 identical with the so-called proper corpuscles 

 of the chyle, surrounded with a membrane 

 which is more or less distended with a red 

 liquid, are met with in the chyle, and occa- 

 sionally, but rarely, in the blood itself. Phy- 

 siologists are not agreed as to the above 

 views, but the preponderance of evidence 

 appears decidedly in their favom'. 



As unusual constituents of blood may be 

 mentioned, — 



1 . Cells, enclosing coloured blood-corpus- 

 cles; found in the blood of the spleen,liver,&c. 



2. Granule-cells, either colourless or con- 

 taining granules of pigment. 



3. Peculiar concentric bodies, three or 

 four times as large as the coloured corpuscles 

 of the blood, resembling those found in the 

 thymus gland. 



4. An unusually large number of colour- 

 less corpuscles. 



5. Pus-corpuscles. 



6. Caudate cells, sometimes containing 

 l)igmcnt. 



7. Crystals of hsematoidine, sometimes 

 within the coloured corpuscles, at others free. 



8. The two molecular substances previ- 

 ously mentioned. 



It sometimes becomes of importance to 

 be enabled to determine the presence of 

 blood, and to distinguish that of man from 

 that of animals. As regards the former 

 point, it is a matter of no great difficulty. 

 When blood has been dried at ordinary tem- 

 peratures, the dried serum and contents of 

 the corpuscles redissolve on digestion with 

 cold water ; and this is the conthtion under 

 which the blood is generally presented for 

 examination in such cases. We then have 

 the fibrine left undissolved, which may be 

 tested as to its chemical and microscopical 

 characters (Fibrine). The liquid is de- 

 colorized by boiling, and the coagulum as- 

 sumes a brown colour (H^ematine). It 

 also contains non, is unaltered in colour by 

 solution of potash, and contains a proteine 

 compound (Proteine). In heating very 

 minute quantities upon a glass slide, the 

 fluid must always be covered with a slip of 

 thin glass, to prevent its drying. The mere 

 presence of blood can thus be chemically 

 determined without much difficulty; for 

 these reactions may be observed under the 

 microscope in a very minute quantity. But 

 the distinction of small quantities of the 

 blood of man from that of animals by chemi- 

 cal means, is impossible. We have therefore 

 only the morphology of the elements to de- 

 cide from. The portions of blood presented 

 for examination will be almost invariably in 

 a dried state ; and the red corpuscles, when 

 dried in a very thin layer, retain so nearly 

 their natural size and outline, that any kinds 

 of blood which are distinguishable in the 

 fresh state, are certainly so when dried. But 

 it will seldom happen that the blood will be 

 dried upon a transparent substance, and in 

 thin layers, permitting of its examination by 

 transmitted light. We have then to separate 

 it from some fabric or structure, and restore 

 as nearly as possible its original appearance. 

 This can be done by digesting the blood in 

 a saturated solution of bichloride of mercury, 

 which has a remarkably slight action upon 

 the corpuscles, allowing both their natural 

 form and size to be judged of with great ac- 

 curacy; and by digesting the blood in a cold 

 solution of this salt, and placing it under abell- 

 glass for some hours, the red corpuscles may 

 be detached with a camel's-hair pencil, and 

 examined. Of comse, only those corpuscles 

 should be measured which evidently retain 



