when is thus rendered once more a vacuum, k and ƒ are opened and more of the air remaining in a, b, d, &c., rushes into the vacuum; f is closed, j is opened, and this air is expelled as before. The process is repeated as often as is necessary to make a, b, d, &c. as complete a vacuum as indicated by the mercury in the gauge, e, as is obtainable.

a being now empty and the stopcock, f, closed, blood is introduced by the tube, e; it froths and gives off all its gases, especially if heated to 40°-45° C. In

the case of serum, acid has to be added to disengage the more firmly combined carbonic acid. The bulb, 7, is once more rendered a vacuum and k and ƒ are opened, j being closed; the gas from a and brushes into the bulb, 7, being dried as it passes through d; f is then closed and j opened; the reservoir, o, is raised, and as the mercury in / rises simultaneously, it pushes the gases into the

1 Phosphoric acid is usually employed.

cylinder, h, which is filled with mercury and inverted over the end of the bent tube. This gas can be subsequently analysed. By alternately raising and lowering o and regulating the stopcocks in the manner already described, all the gas from the quantity of blood used can be ultimately expelled into h.

C

2

a

The large number of stopcocks and joins in Pflüger's
pump (for all the parts can be separated) renders
A good grease for the taps
leakage apt to occur.

will be found to be a mixture of two parts vase-
line to one of white wax. Alvergniat's pump has the
advantage of fewer connections, and all of these are
surrounded by mercury, which effectually prevents
leakage; it has the disadvantage of a rather small
bulb in place of 1, and thus it is more labour to obtain
Dr. McKendrick has also described and

a vacuum.

figured a small and convenient pump.

In the investigation of the gases of muscle the form of receptacle used is here figured (fig. 15): a is a glass bulb into which the muscle contained in boiled salt solution is placed; it is termed the boiling-flask, and is separated from the froth-chamber, b, by a tube provided with a stopcock. a is perforated by platinum wires which can be attached to a battery and thus stimuli sent into the muscle to cause it to contract if required; serves a second purpose besides that of froth-chamber; a reagent, such as an acid, may be kept in it during the preliminary exhaustion of the muscle in a, and then, by tilting the apparatus, may be brought to play on the muscle at any given moment.

FIG. 15.

3.

ANALYSIS OF THE GASES

For gas analysis an accurately graduated and calibrated tube which is closed at the upper end, and then inverted over mercury, is used. It is called a eudiometer, and it has, passing through the glass, two platinum wires which can be connected with an induction coil, and thus powerful sparks can be produced in the interior of the gases is necessary. tube in cases where explosion of

Some gases may be estimated directly, that is, they may be absorbed by certain reagents, the diminution in volume indicating the quantity of gas present. Some are determined indirectly, that is, exploding them with other gases, and measuring the quantities of the products. The gases which are estimated directly are (1) those like hydrochloric acid which are absorbed either by crystallised sodic phosphate or potassium hydrate; (2) those like carbonic acid and sulphurous acid which are absorbed by potassium hydrate and not by sodic phosphate; and (3) those which are absorbed by neither of these two 1 Bert, Leçons sur la respiration, Paris, 1870.

2 Brit. Med. Journ. Aug. 18, 1888.

reagents, but by others specially adapted to meet the case in question; in this class of gases are oxygen, carbonic oxide, nitric oxide, and many gaseous hydrocarbons with the exception of marsh gas. The gases estimated indirectly are hydrogen, nitrogen, marsh gas, carbonic oxide, and several others. As an instance of this last class, hydrogen may be selected; a known volume of oxygen is mixed with it in the eudiometer, and exploded; water is formed which condenses, the remaining oxygen is estimated directly; the loss of oxygen after explosion must be that quantity which has combined with hydrogen ; and knowing the proportion of hydrogen and oxygen in water, the hydrogen can be thus ascertained.

As has been stated already, the physiologist has to deal chiefly with three gases: oxygen, carbonic acid, and nitrogen. The first two can be estimated directly by absorption, the residue is nitrogen.

The tube containing the gases is made to stand in a well-shaped pneumatic trough filled with mercury, and by the aid of a pipette turned up at the end, about half a cubic centimetre of strong solution of caustic potash (sp. gr. 1-2) is introduced; when absorption is complete, and this can be hastened by alternately raising and lowering the tube in the mercury, the loss of volume gives the quantity of carbonic acid previously present. About half a c.c. of strong pyrogallic acid (1 of acid to 8 of water) is then introduced; by this reagent the oxygen is absorbed; and the residue is nitrogen.

Greater accuracy, however, is obtained by using solid instead of liquid reagents. The solid is made into the form of a bullet, which can be introduced by a platinum wire through the mercury into the mixture of gases, and withdrawn when no further diminution of volume takes place. Thus, bullets of caustic potash are used for absorbing carbonic acid; for oxygen, phosphorus was formerly used, but now papier-mâché balls moistened with a freshly prepared alkaline solution of potassium pyrogallate are more generally employed. As a rule these solid substances must be left some hours in the gas before absorption is complete.

Using liquid reagents I have found that the principal tube of Lunge's nitrometer gives very accurate results, and the way I have been accustomed to use it is as follows:

The apparatus consists of an accurately graduated tube a, which tapers at its upper end, and then again widens into the tube b; in this narrow neck is a stop-cock, which is perforated by holes in such a way that in one position (see A) a and b are put into communication with one another; and in another position (see B) b is put into communica

D

tion with the air, or with any other vessel by means of an india-rubber tube d.

a is filled up to the stop-cock with mercury, and placed in a trough containing mercury. The whole apparatus can be raised and lowered by a rack and pinion arrangement, such as one uses to raise and lower

Ъ

a

d

FIG. 16.

a

a

B

the tube of a microscope. The stop-cock e is placed intermediate in position between A and B, so that a is in communication The gas neither with b nor d.

to be analysed is then introduced A into the tube a in one of two ways either through the mercury at the lower opening of the tube ; or by placing the interior of a into communication with a vessel containing the gases, by means of a tightly fitting indiarubber tube d, the stop-cock being placed in the position B; at a given moment, a clip is removed from the tube d, and the gases pass into a, the mercury falling in that tube until it has the same level outside and inside. The

clip is then replaced, the stop-cock once more put in a neutral position, The whole tube is now raised so that and the volume of gas read off. the mercury within it stands at a higher level than that outside. About half a c.c. of strong potash solution is put into the tube b, the stop-cock turned into the position A, and the potash trickles through into the tube a; this absorbs the carbonic acid, the apparatus is then adjusted so that the mercury within and without a is at the same level; and the remaining gases read off. The oxygen is then absorbed by running in pyrogallic acid solution in the same way, and the residual nitrogen read off over mercury, or better over water; in the latter is read off in the moist state and the water within and case, the gas without the tube a must be at the same level.

In order to get results which are comparable with one another, the alteration in the volume of gases produced by temperature, barometric pressure, and if moist, by tension of aqueous vapour must be always allowed for, and the volume corrected to standard pressure (760 mm.) of mercury, and standard temperature (0° C.). The following formula serves for correcting volumes of gases:

B = height of barometer (which should in very accurate
work be also corrected for temperature).

t = temperature in degrees centigrade.

Ttension of aqueous vapour in millimetres of mercury
at t (see table, p. 5).

The number 0-003665 is the coefficient of expansion of gases.

The number 760 × (1 + 0·003665ť) is obtained from tables, and the calculations are much simplified by the use of logarithms: thus,

log Vlog V + log (B-T)—log [760 × (1 +0·093665t)],

or, for dry gases,

log VlogV + log B-log [760 × (1 + 0·0036657)].'

1 Mr. F. Sutton, Norwich, will forward a copy of these tables, printed separately for laboratory use, to any one desiring them, on receipt of the necessary address.