A larger quantity of fibrin has been ob tained by some analysts from arterial than from venous blood in inan and in the domes ticated animals; others again have procured a larger quantity koin venous than from arterial blood; while a few have obtained dissimilar results in their analyses of these two kinds of blood in different genera of animals, and even in different individuals of the same species.* In the greater number of the analyses, however, rnore fibrin was obtained from arterial than from venous blood.± According to Denis and Scherer, the fibrin of the two kinds of bloocl differs in regard to its solubility in nitre. When a portion of well-washed fibrin from venous blood is triturated with a third part of nitre, and four times its weight of water, and a small quantity of caustic potass or soda is then added, it dissolves into a gelatinous mass, having the chemical characters of albu men ; while the fibrin from arterial blood si milarly treated undergoes no such changes.
The blood-corpuscles are more abundant in arterial than in venous blood, according to Prevost and Dumas, Lecanu and Denis ; ac cording to Meyer, Hering, and Nasse, they are more abundant in the venous blood ; while the analyses of Letellier and Simon tend to show that the proportion is fluctu ating. According to Simon, the blood-cor puscles of arterial contain less hmmatin than venous blood, while the quantity of globulin is variable. Mulder states that the chemical composition of hwmatin is the same whether derived from arterial or venous blood.t The statements made regarding the relative proportions of the albumen, fat, osmazone, and salts in the two kinds of blood, differ too much to justify us in attaching any importance to them,— a remark which, as yet, we are afraid applies with too much truth to most of the other statements regarding the che mical differences between the two kinds of blood, mentioned above. Michaelis*, and Marcet and Macaire±, in their ultimate or elementary analyses of both kinds of blood, found more carbon and less oxygen in ve nous, and less carbon and more oxygen in arterial blood ; but Berzelius has adduced sufficient reasons to induce us to doubt whe ther, in such investigations, at least as at present conducted, the distinctive characters of the two kinds of blood can be preserved during the analysis, and that they are de serving of any confidence.t A larger quantity of fixed carbonic acid has been obtained from venous than from arterial blood by Mitscherlich, Gmelin, and Tiedemann.§ It is now placed beyond dispute that free gases exist in the blood, and it be comes a point of great importance in de ciding upon the true theory of respiration to ascertain their nature, quantity, and rela tive proportions in the two kinds of blood. Four methods .have been followed in pro curing the free gases from the blood. 1. By the application of heat. 2. By the use of the air-pump. 3. By agitation of the blood with other gases. 4. By the respiration of other gases than atmospheric air.
The first of these methods is imperfect, as the albumen coagulates when the temperature is raised towards the boiling point, and may retain gases present in the blood. The se cond method is also liable to lead to negative results, unless the air-pump employed be of the best construction, for, according tq Mag nus, it is not until the pressure of the air within the bell-glass is reduced to one inch, that the gases begin to escape from the blood. In such experiments it is also necessary to employ blood from which the fibrin has been retnoved, for coagulated blood will retain the free gases, and prevent their escape.
Sir H. Davy stated that by raising the temperature gradually to 200 Fahr., he ob tained from 12 cubic inches of the arterial blood of a calf 1,16 cubic inch of carbonic acid gas, and of a cubic inch of oxygen!' ; and that he procured carbonic acid gas from human venous blood heated to 112 Fahr.lf Enschut assures us that, by subjecting blood to the temperature of boiling water, he ob tained carbonic acid gas both from venous and arterial blood, and a greater quantity from the former than the latter kind of blood.* It is alleged that Brande obtained carbonic acid gas both from venous and ar terial blood in considerable quantity by the use of the air-pump ; and Scudamore states that he procured it by the. same means in variable quantities from venous blood.$ Col lard de Martigny§ and Enschutil procured carbonic acid gas both from venous and arterial blood, by placing them in the Torri cellian vacuum, and a larger quantity from the former than from the latter. Nasse, Stevens**, Dr. G. Hoffinan ft, Enschut Dr. Maitland §§, and Bischoff II, obtained carbonic acid gas from venous blood on agitating it with hydrogen, or by allowing this gas to stand over the blood for several hours. The existence of free carbonic acid gas in the blood was still, however, regarded by some physiologists as very problematical, since se veral trust-worthy and careful experimenters, such as Dr. J. Davy IN, lsrlitscherlich, Gmelin, and Tiedemann*, Stromeyer Muller and others$, failed in obtaining any carbonic acid gas from the blood by the air-pump and other means, and it WaS not until the publication of the important experiments of Magnus, con firmed as they have been to a certain extent by other observers, and strengthened by evi dence collected both before and since on the results of the respiration of animals in hy drog,en and nitrogen gases, that the existence of any free gas in the blood has been gene rally admitted. Bertuch and Magnus pro
cured carbonic acid gas from human venous blood by agitating it with hydrogen.§ Mag nus has not only obtained carbonic acid gas from both kinds of blood in some of the domesticated animals, but also oxygen and azote by means of the air-pump. The two latter gases were also procured from both kinds of blood by agitation with carbonic acid gas. The quantity of gases obtained from the blood by the air-pump in these expe riments by Magnus amounted to ,tirth, and sometimes to ith of the volume of the blood employed ; but from the difficulty of libe rating the gases from the blood, he believes that this quantity forms but a small part of that actually held in solution in this fluid. In some experiments with hydrogen, the quan tity of carbonic acid obtained amounted to ith of the volume of the blood employed. The relative quantity of oxygen gas to the car bonic acid gas is greater in arterial than in venous blood. In venous blood the oxygen was as ith, and often ith, while in arterial blood it was at least as id and sometimes to the carbonic acid.ji Magnus, in a second memoir on this subject, states that be obtained the following quantities of oxygen and nitrogen from the arterial blood of two old horses, by agitating it in carbonic acid gas :— By adding together the total quantity of gases collected from each kind of blood in his dif ferent experiments by means of the air-pump, and then comparing the relative proportions of their constituent parts, the following results are obtained : — The quantity of oxygen gas procured from the blood of calves, oxen, and horses, pre viously agitated with atmospheric air, was not less than 10 per cent. and not more than 12 per cent. The blood can, however, absorb a greater quantity of oxygen and nitrogen than was collected in the experiments last-men tioned, for by repeatedly shaking blood with renewed quantities of carbonic acid gas to remove the whole of the oxygen and nitrogen gases it contained, and then agitating it in measured quantities of atmospheric air, he ascertained, by again measuring the atmo spheric air, that the minimum quantity of oxy gen absorbed amounted to 10 per cent., and the maximum to 16 per cent. The quantity of nitrogen procured in numerous experiments on the blood of calves, oxen, and horses, pre viously agitated with atmospheric air, was, when reduced to the temperature of 32 Fahr. and the mean barometric pressure, from 1'7 to 3.3 per cent. of the volume of the blood employed. The quantity of oxygen gas which blood is capable of absorbing from the atmo spheric air, is, according to Magnus, from 10 to 13 times more than water can do under the same circtunstances.t The experiments of Dr. J. Davy, Mitscherlich, Gmelin and Tiedemann, Enschut and Magnus, prove that venous blood can absorb considerably more than its own volume of carbonic acid gas ; and according to Mitscherlich, Gmelin and Tiedemann, and Enschut, more of this gas can be absorbed by arterial than by venous blood.* Lehmann has endeavoured to ascertain the relative quantities of free and combined car bonic acid in the blood. In twelve experi ments upon bullock's blood the average quan tity of free carbonic acid in 1000 grammes (15433'0 Troy grains) of blood, was 0'132 gram. (1-937 grains) of free, and 0'6759 gram. (10431 grains) of combined carbonic acid : or, estimating these quantities by volume, in 61'250 English cubic inches of blood, there were 4'271 cubic inches of free, and 21'968 cubic inches of combined carbonic acid.t The results obtained on causing animals to breathe gases devoid of oxygen are in unison with those derived from direct experiment, and furnish additional evidence in proof of the existence of free gases in the blood. That a quantity of carbonic acid gas may be exhaled from the blood during the respiration of gases devoid of oxygen is proved by' the experiments of Spallanzani* and Dr. W. F. Edwardst on the products of the respiration of snails con fined in hydrogen and azote ; those of Dr. W. F. Edwards I on a fish (Cyprinus aureus) confined in water saturated with hydrogen ; those of Dr. W.F. Edwards §, Collard de Mar tigny ji, Milner and Bergmann IT, Bischoff** and Marchand tt, on fi'oo.s confined in hy drogen or azote ; and thsose of Dr. W. F. Edwards TT, upon the younr, of certain of the mammalia confined in hydrogen gas. The experiments of Nysten §§, in which he first exhausted the air, as far as possible, in the lungs of adult dogs, and then caused them to breathe hydrogen or azote; and those of Sir H. Davy II II , and of Coutancean and Nysten on the respiration of nitrous oxide and azote in their own persons, though not free from serious objections, are still, as far as they go, in favour of the opinion that free carbonic acid gas is contained in the blood.