The phosphate of

blood can

not be re

placed by

phosphate

of potash.

tion with phosphate of potash or with earthy phosphates, the phosphate of soda of the blood.

That phosphate of soda is indispensable to the soda in the normal constitution of the blood, and that the processes which go on in that fluid cannot be replaced by phosphate of potash, seems to me to be an opinion fully justified by the properties of these two salts. Through the blood, the carbonic acid formed in the body is conveyed out of it, and the alkaline Importance quality of the blood has a very decided share in its taining the property of thus taking up carbonic acid; as, on the other hand, the chemical nature of the compound, on which the alkaline reaction of the blood depends, exerts the most marked influence on the power of the blood, again to give off the carbonic acid which it had absorbed.

of ascer

true cause

of the alkalinity of the blood.

Relation of blood to carbonic

acid gas.

Experiments of Scheerer.

It is known that freshly-drawn blood, by mere agitation with air, by passing through it a current of hydrogen gas, or in the vacuum of the air-pump, gives off carbonic acid. From the experiments of Scheerer, at which I had the opportunity of being present, and of others, it is known, moreover, that, for example, the clear serum of ox blood, free from blood corpuscules, absorbs nearly twice its volume of carbonic acid, that is, as much more as the same bulk of water can absorb at the same temperature. The greater absorbing power of the serum is determined by a chemical attraction, by a substance, which has an alkaline reaction. In fact, it is observed, that, when this alkaline reaction is destroyed,

when acetic acid is added to the blood saturated with carbonic acid, the excess of carbonic acid is at onee given off. But the same thing happens when this blood is agitated with gases, such as hydrogen, for a long time, and the gases renewed from time to time.

Blood, when not saturated with carbonic acid, gives off, in vacuo, nearly 5 p. c. of its volume of that gas; the addition of acetic acid increases the quantity of the carbonic acid disengaged; but even under these circumstances not more than half its volume of carbonic acid can be obtained from blood. Had the greater absorptive power of the serum of blood for carbonic acid been dependent on the presence of carbonate of soda, and its conversion into bicarbonate of soda, this would imply that the blood must contain at least its own volume of carbonic acid in the form of neutral carbonate of soda. If blood contained its own volume of carbonic acid in the form of neutral carbonate, and no free carbonic acid, this blood would absorb exactly twice its volume of carbonic acid (one volume to form bicarbonate, the other to saturate the liquid as it would an equal bulk of water), and the addition of acids which decompose the carbonate of soda, must, in that case, disengage a volume of carbonic acid equal to twice the volume of the blood. The acid would, in fact, disengage three volumes of carbonic acid, one of which is retained by the liquid. In the experiments of Scheerer, serum of blood, which

I

The serum contains no

of blood

carbonate

of soda.

The author's experiments to prove this.

had absorbed twice its volume of carbonic acid, only yielded half as much carbonic acid as ought to have been given off on the above supposition. There was less than one volume of free carbonic acid present in the serum, and the liquid retained, for that reason, a proportionally greater quantity of carbonic acid.*

When 2,000 cubic centimetres of ox-blood, mixed with twice their volume of water, are heated to boiling, and the coagulum pressed out, we obtain about 2,000 c. c. (1-3rd of the whole liquid) of an alkaline liquid. If the alkaline reaction of this liquid arises from carbonate of soda, these 2,000 c. c. must contain 1-3rd of the whole carbonate of soda contained in that volume of blood. When concentrated to 1-3rd by evaporation, this liquid must contain exactly as much, if concentrated to 1-6th, twice

* Annalen der Chemie und Pharmacie, vol. xl. p.

30.

I. 60 vols. of serum absorbed 124 vols. of carbonic acid.

After the addition of 30 cubic centimetres of acetic acid to the first portion, and of 28 c. c. to the second portion of serum, in all after the addition of 58 c. c. of acetic acid, there were disengaged, from 174 vols. of the mixture (116 vols. of serum and 58 vols. of acetic acid) 89 vols. of carbonic acid. Had the blood contained its own volume of carbonic acid in the form of neutral carbonate of soda, it must have given off 177 vols. of carbonic acid; that is, 235-58 (the volume which would be retained by the acetic acid). According to these experiments, the actual amount of carbonic acid present in the blood is calculated to be 28 per cent. of its volume.

as much, to 1-12th, four times as much, and to 1-24th, eight times as much, &c. carbonate of soda as an equal volume of blood.

concen

serum

carbonic

Now, I have concentrated this liquid to 1-500th Highly of its volume, in which state it must, on the suppo- trated sition formerly mentioned, contain 166 times as absorbs much carbonate of soda as an equal volume of blood, acid, if that salt were an ingredient of blood. When brought in contact with carbonic acid, this concentrated liquid absorbed 3 times its own volume; 20 c. c. absorbed 60 c. c. of carbonic acid. Now it is certain that if this absorptive power had been dependent on the presence of carbonate of soda, the solution, saturated with carbonic acid, must have given off, when mixed with acids, 3 times its original volume of carbonic acid, of which 1-3rd would be retained by the liquid. From 20 c. c., therefore, of the concentrated liquid, there should have been obtained 40 c. c. of free carbonic acid. But this liquid, when acted on by acids, gave off no are added appreciable trace of carbonic acid

gas.

but does

not give off a trace

when acids

to it.

According to the observations of Marchand, this liquid is not free from carbonic acid, when it has been mixed with another acid, for by heating it carbonic acid is expelled. But even on the most 7.5 cubic favourable supposition, that is, if we admit that the liquid is saturated with carbonic acid, it is obvious that no more carbonate of soda can be contained in

in ches of

serum can

not contain more than 2-5ths of a grain of

carbonate

it than corresponds to the volume of carbonic acid of soda, required to saturate the 1-166th part of the volume

but it absorbs at least 166

times more

carbonic

acid than

of the serum.

This amounts, for 1,000 c. c. of serum, to so much soda as is saturated by 6 c. c. of carbonic acid gas = 0.026 gm. of carbonate of soda, or 2-5ths of a grain.

The serum of blood absorbs, therefore, 166 times more carbonic acid than could be absorbed by the very largest proportion of carbonate of soda which this carbo- it can be supposed to contain; and consequently the carbonate of soda, if it be present at all in the liquor sanguinis, can have but a most insignificant share in the absorptive power of that fluid for carbonic acid.

nate could.

This de

pends on the phosphate of soda.

As the study of the serum and the analysis of the ashes of blood prove, the alkaline quality of the blood depends on the presence of phosphate of soda. Indeed, it may well be asked, from what source can carbonate of soda, if we suppose it to be present, be derived, in the blood of a man living on bread and flesh, or of an animal feeding on flesh, since in these kinds of food the alkalies and phosphoric acid are present in the proportion in which they form salts with 2 and with 3 atoms of fixed base ?*

* The experiments of Erdmann on the incineration of wheat (Annalen der Chemie und Pharmacie, vol. liv. p. 354) leave no doubt, that the tribasic phosphates (with 3 atoms of fixed base) in these ashes are derived from the action of carbon on the phosphates with 1 and 2 atoms of fixed base, at a red heat, or from the decomposition of chloride of sodium in contact with these phosphates. In the analyses of Henneberg, where this last cause was avoided, the formation of pyrophosphate of soda proves, that the blood of fowls contains tribasic phosphate of soda with 2 atoms of fixed base (P O5, 2 Na O, H O).