Chlorosis.—Among other changes which oc cur in the progress of chlorosis, there is none more constant than an impoverished condition of the blood, which is thin, light-coloured, and weakly coagulable, being deficient in fibrine, and still more so in the proportion of the red par ticles. To the latter cause is to be attributed the diminished temperature of the surface, to gether with the universal pallor and waxy ap pearance which those who are the subjects of this disease generally exhibit. The deficiency of colour in the catamenia, and the pale stain which hemorrhages from the nose leave on linen, are also referable to the same cause. In aggravated cases, if blood be drawn from the arm, the crassamentum is observed to be of a pale rose colour, and small in proportion to the serum. We have to regret that in this, as in most other cases of morbid blood, pathologists have contented themselves with a general ob servation of facts without attempting to inves tigate them with that degree of precision which can alone lead to a further advancement of our knowledge respecting their causes. The only analyses of chiorotic blood of which I can find a record are given by Mr. Jenkins in two well marked cases of chlorosis ; the one of a girl aged fifteen, the other of a young woman aged twenty-one. In these the blood contained 871 and 852 parts in a thousand, of water, respec tively, instead of 780, the healthy standard; and the colouring matter amounted to 481 and 52, instead of 133. The albumen and salts were in the usual proportions.
lifelanosis.—Although it would be foreign to my present object to treat of the various morbid products which may be supposed to have their origin in a diseased state of the blood, yet there is one which seems so evidently to be the result of an accidental change in that fluid, that it must not be passed over without a brief notice. The similarity of chemical composition in the blood and in the matter of melanosis is such as to leave little doubt that the material of which the latter is composed has its origin in the circulation, and is afterwards deposited in the various parts in which it is found. The different analyses of melanosis, says Andral, all concur in one important point. They all shew that the accidental production called melanosis is formed of the different elements of blood, and especially of a colouring matter which more or less resembles that of the blood, but which is, nevertheless, not identical with it. M. Foy, in his analysis, calls this altered cruor. Dr. Carswell, to whom we owe the most detailed and best account of melanosis which we possess, states that he has fixed its seat in the blood, not only because it is seen there, but because his anatomical researches shew that it is there formed. He makes a grand division of melanosis into true and spurious ; the former of which occasionally makes its appearance in the circulating system, a fact which is well established, while the latter is more decidedly the result of chemical action. Whenever healthy blood comes in contact with an acid, whether in or out of the body, its colour changes from red to brown or black, in proportion to the strength and abund ance of the acid employed. It is to this cause that we are to attribute the appearance of brown or black ramifications, patches, or points, as ob served after death in the stomach and intestines. To this cause also are owing the accumulations, during life, of black pitchy matters in the ali mentary canal, and it is by the acidity of the black vomit and its power of reddening litmus paper, as we learn from Dr. Stevens, that it
can alone be distinguished from blood rendered black by defective decarbonization or the ab sence of saline ingredients. Where a rhage occurs, whether by the rupture of a large vessel or by a general oozing from the mucous membrane into the stomach or bowels, we shall find the fluid ejected assume the appearance of red blood or of brown or black matter, accord ing to the presence or absence of the gastric juice in an acid state. Upon this almost acci dental circumstance, then, will it depend whether we are to designate the disease hTmatemesis or melaena, there being in reality no essential dif ference between the two diseases. The black discolouration of blood which occurs whenever it becomes stagnant from retarded or interrupted circulation, will, by those who follow the views of Dr. Stevens, be attributed to a similar cause. According to that author it is the presence of carbonic acid which acts like other acids in ren dering venous blood dark, and it is its abstrac tion by oxygen which, combined with the action of the saline matters it contains, restores it to its scarlet hue.
The foregoing are among the more pro minent diseases in which the blood has been observed to undergo changes either directly cognizable by our senses, or discoverable by those chemical and mechanical means which we are enabled to call to our assistance. There are, however, other morbid conditions the ex istence of which is equally certain, although their essence is of such a doubtful nature that it defies detection by the coarse instruments and the limited skill which man, in the present state of his knowledge, is enabled to employ. In the exanthematous diseases the blood par takes of the general disorder of the system. Dr. Home of Edinburgh* succeeded in reproducing measles by inoculation with blood drawn from a superficial vein in one of the patches of eruption which cover the skin in that disorder ; and though others have failed in this experi ment, it has been successfully and often re peated by Professor Speranza of Mantua. Pregnant females affected with small-pox, or even exposed to its virus, though they may have had the disease, have often imparted it to the foetus in utero,t and syphilis has been communicated in the same manner. Professor Coleman has proved by experiment that the blood of a glandered horse will impart glan ders if infused into the veins of a healthy animal. Dupuy and Leuret have thus pro duced malignant pustule ; transfusion of the blood of a mangy dog has produced mange in another; and, according to Dr. Hertwich of Berlin, the blood of a rabid animal will by inocu lation communicate the disease. A remarkable instance is related by Duhamel, in which a butcher became affected with a malignant pus tular disease in consequence of having put into his mouth the knife with which he had slaugh tered an over-driven ox. Another individual lost his life from sphacelus of the arm in con sequence of a wound in the palm of his hand, accidentally inflicted by a bone of the same animal; arid in two women who received some drops of its blood, the one on her hand, the other on her check, inflammations ensued which rapidly terminated in gangrene.