BLOOD. 



527 



Many experiments have, since the improvement of 

 pneumatic chemistry, been made with a view of 

 ascertaining the action of different gases on the 

 blood, but the performance of such experiments is 

 rather a nice operation, and when they are performed, 

 they are of no great value, because, in the living 

 subject, gases do not come into contact with the 

 naked blood. The place where any gas comes most 

 nearly into contact with the blood of animals is in the 

 breathing apparatus, whether lungs or gills, and the 

 explanation of the action there is one part of what 

 we propose to reserve till the article CIRCULATION. 

 We may, however, in the meantime, mention gene- 

 rally, that oxygen appears to retard the process of 

 coagulation, but that it is accelerated by carbonic 

 acid, and by all the gases generally which are unfit 

 for the purpose of respiration ; that the application of 

 oxygen tends to heighten the scarlet colour of the 

 blood, but that those gases which accelerate the 

 process of coagulation tend to make the colour 

 darker and blacker. The effect of oxygen may be 

 seen in any case where blood is allowed to coagulate 

 exposed to the atmosphere, for in such cases the 

 upper, or exposed surface, is of a very intense and 

 beautiful red, while that which is below, and with 

 which the air does not come in contact, is of a more 

 dingy hue. . Whether, in this case, the oxygen of the 

 air produces the same effect upon the blood as it 

 does when applied through the coats of the pulmonary 

 vessels in the process of respiration that is, whether 

 it attracts carbon from the blood, and forms carbonic 

 acid with that carbon, is not exactly known, but 

 there is a specific difference between the action of 

 oxygen upon blood when out of the vessels and when 

 in them. In both cases the colour of the blood is 

 changed to a finer red by the action of the oxygen ; 

 but while that gas retards coagulation in blood 

 exposed to the free air, it appears to accelerate the 

 same operation in the vessels ; for arterial blood 

 coagulates sooner and more readily than the darker 

 blood of the veins, although, when a coagulum 

 once forms in the darker-coloured venous blood, it is 

 of much firmer consistence. 



Why the case should be different with blood ex- 

 posed to the free air has not been very satisfactorily 

 explained, but one can very readily see the advantage 

 of the effect produced by oxygen upon the blood 

 within the vessels. The more readily that the blood 

 coagulates when taken out of the system, the more 

 easily must it come to that state in which it forms 

 into fibrin in the system ; and the less completely 

 that it passes into a solid coagulum, the greater may 

 we suppose to be its susceptibility to vital action ; for 

 coagulation is the state of final and irreclaimable 

 inertia in the blood, except in those cases of violent 

 action in which the crassamentum is broken down, 

 and the power either of forming fibrin or of coagulat- 

 ing prevented. 



Tiie red particles of the blood which, along with 

 fibrin, or matter disposed to form fibrin, make up the 

 whole volume of the crassamentum, or clot, have, as 

 is the case with all natural substances, the use of 

 which is not very well known, given rise to much 

 speculation. According to what may be considered 

 the most accurate measurement of these particles, 

 they do not exceed the two-hundredth part of an inch 

 in diameter, and therefore they fall under the deno- 

 mination of objects wholly microscopic, the descrip- 

 tions of which are always to be received with caution, 



as the refraction, and other colouring tendencies of the 

 instrument, are apt to change both the apparent she 

 and the apparent colour of that which is -een through 

 it. There have been many differences of opinion 

 about the size, the form, and the use of these particles, 

 but none of them are very satisfactory, and they are 

 too minute for enabling us to hope for any thing very 

 conclusive. They are said to differ in magnitude 

 and also in form, not only in different animals, but in 

 the same animal during different stages of its develop- 

 ment. 



Though the use of these red particles in the animal 

 economy is not known, and though no satisfactory 

 inference can be drawn from the examination of 

 bodies in themselves so minute, unconnected with the 

 system and with each other, any farther than that they 

 float in the blood, intimately and equally distributed 

 through its mass in ordinary and healthy states, 

 attaching themselves in the fibrin when "it forms 

 either into clot or into a fibrous consistency, and 

 tending to precipitate in those inflammatory states of 

 the blood in which it shows the bufty coat when 

 drawn from a vein ; yet they must answer some very- 

 important purpose connected with life and living 

 action in those animals which have their organisation 

 much developed. Little knowledge can be hoped to 

 be obtained from an examination of their forms, or of 

 their chemical composition as matter ; for the inves- 

 tigation of living action, and the means by which that 

 action is performed, is an investigation of connections, 

 not of single parts of relations, not of forms ; and 

 when they are in such a state as that we can obtain 

 any, even the slightest knowledge of their chemical 

 properties, they are out of their connection ; the 

 relation between life and them is at an end ; they can 

 be examined as dead matter only ; and all the conclu- 

 sions at which we are capable of arriving, relate only 

 to the part which they are capable of performing in 

 the economy of dead matter. 



It has been said that these minute particles, or 

 globules (for even their figure is not fully ascertained), 

 consist of an external coat or tunic, a contained fluid, 

 and a central nucleus. If such be the case (for even 

 this is obscure), there is in them some resemblance in 

 arrangement of parts to that which occurs in an egg ; 

 and as probably the majority of the eggs of animals 

 are stimulated into action by external causes, we might 

 perhaps conclude that those red particles of the blood 

 form the portion of it which is most sensible to such 

 causes, and which, easily excited in itself, extends 

 excitement to the rest of the system. But the analogy, 

 even if it were good for any thing, fails, because these 

 particles are certainly not germs of any kind, and out 

 of the system they resign themselves to that chemical 

 decomposition to which all organic matter is subject 

 when the life which it once exercised is at an end. 



It were very desirable to know something about 

 those red particles, because they are common to the 

 blood of all vertebrated animals ; because, as the 

 blood is most abundant in the most perfectly de- 

 veloped races, they must be most numerous in them ; 

 because they contain an ingredient which does not 

 appear to be formed in any other part of the system, 

 at least in such abundance ; and because they have a 

 tendency to separate ffom the blood (at least par- 

 tially) in cases of inflammatory disease; and above all, 

 because it is in them chiefly that the effects of air in 

 the grand operation of breathing are chiefly visible. 

 These considerations bring us apparently so near to 



