BLOOD. 



[ 85 J 



BLOOD. 



subsides ; this consists of some of the albu- 

 men thrown down from the serum, with 

 shreds and walls of ruptured coloured cor- 

 puscles, a few of the latter unaltered, and 

 some unaltered or but slightly changed co- 

 lourless corpuscles. 



xVlmost immediately after the blood of the 

 Vertebrata has left the blood-vessels, it be- 

 gins to coagulate. This coagulation arises 

 from the gradual solidification of the fibrine, 

 which exists in a state of solution in the 

 living iiuid. Within about three minutes, 

 the surface of the coagidating blood becomes 

 gelatinous; in about ten minutes it is gelati- 

 nous throughout, and after a further lapse 

 of time, the coagulation of the fibrine appa- 

 rently attains its maximum : this process is 

 not, however, really completed until from 

 twelve to thirty-six hom's. We then find a 

 firm red clot immersed in a yellowish liquid. 

 The fibrine during its coagulation entangles 

 a large number of the corpuscles, which im- 

 part to it the red colour ; this is greatest to- 

 wards the lower part of the clot. The liquid 

 from which the clot has separated, the serum, 

 also contains some of the globules in sus- 

 pension ; most of those not entangled in the 

 clot, however, subside to the bottom of the 

 vessel. The sp.gr. of the serum is about 1030. 

 The appearances presented under the micro- 

 scope by a drop of coagulating blood are 

 very interesting. If examined immediately 

 aftCF removal from the body, the cor- 

 puscles are seen to be diff\ised irregularly 

 over the field ; but after the lapse of about a 

 minute, the red corpuscles unite by their 

 broad surfaces, gradually arranging them- 

 selves into rows resembling strings of figs : 

 these interlace, forming an irregular red net- 

 work, within the meshes of which the colour- 

 less corpuscles are seen (PL 40. fig. 3/). 

 The latter remain isolated, having no ten- 

 dency to unite with the former. To observe 

 these phsenomena, the thin glass covering 

 the di-op of blood must not be pressed down, 

 othermse the free motion of the corpuscles 

 will be impeded. After a time, the fibres 

 break up, and the corpuscles float separately 

 in the serum. 



The coagulated fibrine is also seen distri- 

 buted over the field, partly in a granidar 

 form, but mostly in that of a network of 

 very delicate fibres. Sometimes this running 

 together of the red corpuscles begins to take 

 place immediately the blood has left the 

 body, and the rows are seen to be formed 

 very much more rapidly than in the healthy 

 fluid ; and whtrn tliis is the case, the u})per 



siu'face of the clot will be found to be 

 free from the red colour, and more or less 

 cu})ped or concave : this upper layer is called 

 the buff}' coat, and is in general a sign of 

 inflammation. Considerable doubt still ex- 

 ists in regard to the nature of this buffy 

 coat. It is also met with in blood which has 

 been covered with a layer of oil before co- 

 agulation. But in the natural state it arises 

 from the subsidence of the corpuscles before 

 the commencement of the solidification of 

 the fibrine, whereby the particles of the lat- 

 ter are brought into closer contact, thus al- 

 lowing of its greater contraction. Certain 

 salts prevent the separation of the fibrine in 

 the form of fibres, and cause it to assume 

 the form of minute granules or glo- 

 bules. 



In addition to the corpuscles above de- 

 scribed v.hich are constantly found in the 

 blood, it sometimes contains globules of oil, 

 and, after meals especially, two distinct kinds 

 of a white, extremely fine molecular sub- 

 stance ; one consisting of fat, the molecular 

 base of the chyle, the other a very finely di- 

 vided albuminous substance. They render 

 the blood milky in appearance. The di- 

 stinction of the molecular base of the chyle 

 from the molecular albuminous deposit must 

 be eff'ected by setlier, which dissolves the 

 latter but not the former; but great care 

 is requisite in judging of the action of 

 aither. 



The colour of the blood of the Vertebrata 

 varies according to whether it is removed 

 fi-om the arteries or the veins, in the former 

 case being of a much lighter and brighter red 

 than in the latter. It is beyond our ])rovince 

 to enter into the details of the causes of their 

 diff'erence; suffice it to say, that it arises 

 principally from an alteration in the globules, 

 by which they are enabled to reflect light 

 more copiously. 



In the Invertebrata the coagulation of the 

 blood is imperfect, and the clot much less 

 firm and coi)ious than in the Vertebrata. 



The uses of the blood scarcely requiie 

 mention. It is at the same time the nutri- 

 tive fluid from which all the tissues of the 

 body are formed and renovated, and that in 

 which the components of the secretions are 

 produced and from which they are separated. 

 The red particles are subservient to the pur- 

 poses of respiration ; they are most numerous 

 in those animals in which the respiratory 

 function is most active, and which consume 

 the largest proportion of oxygen, as; birdvs 

 and mammalia. 



