We know by observation and experiment that it is the blood that supplies the living tissues with the materials which they assimilate to repair their losses resulting from the vari ous processes of which they are the seat, as well as to add to their masses during the period of their growth; thus, when by mechanical means we lessen in a notable and permanent manner the quantity of this fluid received by any organ, we soon find. it declining in size, and often shrinking almost to nothing; whilst on the other hand we see that the more blood any part receives, the more does it tend to in crease in size. It has also been demonstrated that it is at the expense of the blood that the different glands prepare the fluids they are destined to secrete, for the ligature of the ves sels which run to one of these organs is followed by the immediate cessation of its secreting function. From this it became an interesting question to determine whether or not the blood contains, ready formed, the various substances of which these tissues and these secreted fluids are composed, and if the organs it traverses do anything more than merely separate these from its mass, or whether the general nutrient fluid only supplies to the different parts of the economy the primary elements necessary to the formation of the substances of which we have spoken, which would then be originated by the tissues or glands in which they are encoun tered. To resolve this question, it became necessary to contrast the chemical composition of the tissues and fluids of the economy with that of the blood, and to ascertain whether the last-named fluid contained all the variety of substances which are met with elsewhere in the animal organization.
This very important part of organic chemistry is not yet sufficiently advanced to enable us com pletely to answer the question : all we know, however, goes to prove that the component parts of the tissues and secreted fluids exist in the blood ready formed, and are only sepa rated from its general mass by the organs which at first sight seem to produce them. In the blood we discover—ist, water, an element which enters in large proportion into the com position of all the fluids, and even forms a considerable item in the constitution of all the tissues : 2d, fibrine, which forms the basis of the muscles : 3d, albumen, which is met with in variable but still considerable quantities in the brain, cellular substance, membranes generally, and in the greater number of the secreted fluids which are not excrementitious : 4th, a fatty phosporated matter, which enters into the composition of the nervous system : 5th, a peculiar colouring matter of a yellow hue, which, slightly modified, is perchance the same as the pigmentum nigrum of the choroid coat of the eye, and of melanosis : 6th, phos phate of lime and phosphate of magnesia, salts which form the inorganic basis of the bones : 7th, alkaline salts, which are met with in almost all the fluids of the body 8th, cholesterine, a peculiar fatty matter existing very abundantly in the bile : 9th, urea, a substance characteristic of the urine : lastly, various other matters more or less accurately defined.
Under ordinary circumstances our means of analysis are inadequate to demonstrate the presence of urea in the blood ; but if the ac tion of the organs destined to separate this substance from, its current in proportion as it is formed, be arrested, the amount contained goes on increasing continually, so that before long it becomes easy to distinguish it. Messrs.
Prevost and Dumas have shown that, after the extirpation of the kidneys, the blood always contains urea in appreciable quantity.* This experiment, the results of which have been confirmed by Messrs. Vauquelin and Sega las, is of the highest importance, and shows that if we have hitherto failed to discover uric acid, caseum, and the other compo nent elements of the principal fluids in the blood, we are not, therefore, to conclude that they do not exist there ; analogy would even lead us to infer that they are actually present, and that if we were to interrupt the different glands in the performance of their functions, they would be discovered in appreciable quantity. Experiments con ducted in this view would be extremely in teresting. Another subject of inquiry, too, not less important, would be to discover the source of the gelatine which forms the basis of the cartilages, tendons, ligaments, &c. and which does not appear to exist in the blood.
The most complete analysis of the human blood we possess is that published lately by M. Lecanu, a chemist of Paris.-t- The careful examination of the blood of two strong and healthy men afforded the following results.
Since the publication of the preceding ana lysis, M. Boudet has discovered a new substance in the serum of the blood, which he denomi nates seroline. This is a white slightly opa lescent substance, fusible at 36 cent., (about 94° Fain.), not forming an emulsion with water, soluble in alcohol, not saponifiable, and appearing to contain azote. This chemist has also shown that the oily matter mentioned by M. Lecanu is a mixture of cholesterine and an alkaline soap, similar to that which is met with in the bile ; lastly, he has determined the identity of the fatty chrystallizable phosporated matter contained in the blood with that dis covered by Vauquelin in the brain (cere brine).* The study of the colouring matter of the blood has engrossed a large share of the atten tion of chemists ; nevertheless its nature is still very imperfectly known. It is very com monly designated under the name of hemato zinc or hematine, and can be readily shown to have the greatest analogy to albumen, from which it is indeed always separated with great difficulty. This matter is soluble in pure water, insoluble in serum and in water impreg nated with salt or sugar, coagulable by heat, capable of absorbing oxygen, carbonic acid, and various other gases which modify its colour. According to M. Lecanu the hematine of chemists is a combination of albumen and the pure colouring matter of the blood, which lie proposes to designate globnline.* But his researches into this delicate subject do not seem to us altogether satisfactory, and we have reason to believe that his globuline is neither more nor less than some of the globules of the blood which have escaped the action of the sub acetate of lead employed to precipitate the un combined albumen. However' this may be, the colouring matter of the blood after incine ration leaves a large quantity of ashes, in which a considerable proportion of oxide of iron can be demonstrated, to the presence of which several chemists have ascribed the red colour of the blood ; such an opinion, however, does not seem tenable at the present day.