3. That the reddish, the blackish, and the dark brown colour of pus depends upon the red part of the blood effused or secreted from the same vessels, or from contiguous ones which secrete pus.

4. That on some occasions the clotty and irregular figured masses found in the pus may depend upon disorganization or breach of the contiguous solid parts.

5. That whenever pus is foetid to the smell, a portion of it is in a state of putrefactive fermentation, which may be removed by ablutions with water.

6. That there are certain adventitious matters liable to be contained in pus not hitherto rendered palpable to the senses, but known by their effects in exciting contagious diseases; such as small-pox, syphilis, &c. These matters are produced by a specific action in the secretory organs of pus, by such matters themselves either contained in the circulating blood, or on the secreting surface.

7. That the essential substances of which pus consists, as well as some of the adventitious ones (Sect. VII. 1, 2, 3, 6), are separated from the blood by a peculiar organization belonging, or attached to the blood-vessels: which organs of separation or secretion are not only excited to the action which produces pus in diseased states, but they are evidently influenced by the states of other distant organs of the animal œconomy; hence many varieties in the properties of the pu rulent matter.

8. That the varieties of purulent matter relate to differences of quantity-the proportion of the essential substances (1)and the adventitious parts (2, 3, 4, 5, 6,). The creamlike consisting of almost purely the opaque oxide and limpid liquid (I. 1, 2). The curdy containing a large proportion of coagulated lymph, or broken down solids. The serous abounding in limpid fluid. The viscid depending upon the coagulation, and perhaps, inspissation, by union of neutral salts with the opaque oxide.

9. That as the essential parts are secreted in a limpid state, but presently become opaque, owing to a large proportion spontaneously coagulating, and thus becoming the opaque oxide, mixed with the serous liquid, and innumerable spherical particles (Sect. VII. I. 1, 2, 3), it seems reasonable to infer that these matters are the self-coagulated lymph of the blood and serum, "separated by the secretory organs; which act of secretion determines the subsequent state of aggregation of pus, and the globules are at the same time formed analogously to their formation by other secretory organs. How far they are those of the blood altered by secretion may be determined hereafter. It is a collateral proof of this inference

that

that very thick pus affords one sixth to one seventh of exsiccated brittle residue, which, as I have found, is nearly the same proportion afforded on the exsiccation of the buffy coat of inflamed blood; while very thin pus affords on exsiccation one eighth to one eleventh of brittle residue, which is the proportion to be expected from a mixture of scrum of blood and self-coagulated lymph, as I have ascertained.

10. That the constant impregnating saline and earthy ingredients of pus are dissolved in the serous fluid, and are all separable along with the serum, by ablutions with water, from the opaque oxide (1), except a portion of the phosphate of lime. These impregnations are the same as those of serum of blood, and of expectorated mucous matter, viz. muriate of soda; potash neutralized by animal matter or a destructi ble acid phosphate of lime; ammonia neutralized probably by phosphoric acid; with a sulphate and traces of some other matters mentioned in my former paper. The propor tion of these impregnating substances is as the proportion of limpid or serous coagulable fluid, and of course inversely as the proportion of the opaque oxide of pús; but it varies in different cases in given proportions of this oxide, and the limpid fluid. In general, if not always, a given quantity of pus contains a smaller proportion of saline matters than an equal given quantity of expectorated mucous matter, but a given quantity of the limpid coagulable fluid contains a greater proportion of saline matters than an equal given quantity of serum of blood. Hence the thicker the pus the less irritation to the sore which secretes it, and commonly the less the inflammatory or other action of the secreting surface. In different cases, however, the proportion of impregnating saline substances to one another is liable to vary, especially that of phosphate of lime: hence, though rarely, calculi occur of this substance in the cavity of the abscess*. Hence too the exsiccated pus is liable to become soft and moist, from the proportion of neutralized potash being greater than usual; and even deliquescence sometimes occurs of the exsiccated limpid fluid.

12. That the same organs, according to their different states,

* On examining the lungs of a patient who died of pulmonary consumption, concretions were found in a large vomica from the size of a mustard seed to a pepper corn, which Dr. E. N. BANCROFT reserved for my enquiry. I found they consisted chiefly of phosphate of lime with an unusually small proportion of animal matter. In another patient of Dr. NEVINSON, matter was coughed up, consisting chiefly of phosphate of lime and animal matter; nearly one of the former to three of the latter.

(No. 146.)

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secrete

secrete from the blood merely water impregnated with the saline substances of the serum of blood; also this fluid containing various proportions of coagulable matter like that of serum of blood; and serous fluid with self-coagulable lymph, which affords curdy masses: likewise this serous fluid, together with this matter which coagulates of itself after secretion, highly impregnated with invisible small particles, in such a state of aggregation, as to constitute the thick opaque fluid called pus-which states of the secretory organs are generally attended with inflammatory action, but frequently also without any symptoms of such action.

13. That besides the consistence of pus depending upon the proportion of serous limpid liquid, and opaque matter, it also probably depends upon the mode and state of coagulation of the matter which affords this opaque part; analogously to the different states of consistence of the coagulated blood itself, according to the different conditions of the ani mal œconomy.

According to the above inferences, I trust, a distinct and definite notion of the substance to be considered as pus is exhibited; and I do not comment on the different results of experiments and conclusions of other writers, because future observers only can determine the truth. What is and what

is not pus will now readily be ascertained by a few easy experiments; by the obvious properties; and by the consideration of the source of the matter in question: provided, however, that it be unmixed with certain other matters by which disguise is produced. As already observed, it is in pulmonic diseases that the ambiguity occurs; and physicians lay very considerable stress upon the nature of expectorated matter in their practice and reasoning; I shall therefore endeavour to elucidate the subject by remarks on the puriform matter expectorated in different cases.

1. An abscess occasioned by acute inflammation not only of a pleurisy, and peripneumony, but of other diseases which have not the symptoms of any one which has received a designation. Here there ought to be no doubt; for the matter which is coughed up suddenly and abundantly on the bursting of the abscess is evidently pus with little mucus. Such matter consists of the essential ingredients of pus, (Sect. VII. 1,) with generally adventitious substances, (Sect. VII. 2, 3, 4,) viz. coagulated lymph, membranous or fibrous parts, and a small portion of the red part of blood.

2. Purulent expectoration from the rupture of abscesses, or vomicæ of suppurated tubercles. In such cases there has been a chronical cough with viscid sputum, commonly in persons of an advanced age. After this long continued dis

ease,

ease, and abundant expectoration of quite a different kind from the former suddenly comes on; by which the patient often dies very speedily; sometimes immediately, being seemingly choaked. This kind of matter evidently consists chiefly of the essential ingredients of pus (Sect. VII. 1,) with: not only the adventitious substances, viz. clots of self-coagulated lymph, and sometimes the red part of blood, but also masses, which are apparently the broken down solid parts, the cellular membrane, the vessels, and substance of the tu bercles, in a disorganized state. The sufferer often says, such matter tastes sweet. The mucus is here in too small a proportion, and not intimately mixed, to occasion disguise.

3. In the bronchitis, or inflammatory affection of the airtubes, the membrane remaining entire, attending various diseases, e. g. the measles, a fever with a cold, various continued fevers, an expectoration of thin cream-like matter occurs, at first gradually, but at last in great quantities, continuing for a week or more. Although mucus is usually coughed up with this puriform substance, the two things generally remain in distinctly large masses. With little skill, the opaque or puriform fluid may be collected separately from the mucous matter. It will be found to consist almost purely of the three essential constituents of pus (Sect. VII. 1,) there being seldom any adventitious sub

stances.

4. Muco-purulent, or commixed expectorated matter. This kind is perhaps of the most frequent occurrence. It is that which many physicians know not how to designate; some consider it to be pus, and others to be mucous matter. This contrariety of opinion arises from the want of definite notions of pus and mucus. Hence the parties are not able to perceive that in this kind of sputum, exist many of the properties of pus, and also of mucus. Í have described it in my former paper on expectorated matter, Phil. Trans. 1809, P. II. p. 317, under the denomination of opaque ropy matter, the third kind. I feel no degradation in finding it necessary to confess, that a better acquaintance with the properties of pus has taught me that I was in an error, in considering this kind of expectorated matter to differ from other sorts, merely in the proportion, and not in the kinds of constituent parts. It now appears, that the sputum in question possesses such properties as might be predicted to exist, from the known properties of pus and mucus separately, in case these two substances should be intimately commixed. Accordingly, the opacity; the straw colour; the greater, density than mucus; the great globularity under the microscope;

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the

the greater proportion of residue on evaporation to dryness, than from mucus; the milky liquid on heating this matter;. the milkiness on agitation in cold water; are properties of pus. But the great viscidity, yet not increased by neutral salts; the less opacity than pus; the less globularity-than pus; the smaller proportion of exsiccated residue than from pus; the moisture, or greater moisture on the exposure of the brittle residue to air, than from that of pus; the more difficult diffusibility through cold water, and less degree of milkiness than from pus; the great proportion of leafy or fibrous masses on agitation in a very large quantity of cold water; the speedy putrescency; are properties of mucus. The mode of coagulation by caloric at 160° and upwards, is such as might be expected from the commixture, viz. in large masses of curd in a milky liquid, instead of into one uniform mass like pus, or into small curdy masses in a very large proportion of whey-coloured liquid, like mucous sputum. Thick pus affords on evaporation to brittleness, or residue; and transparent sputum of the consistence of jelly, gives about or of such residue; but this opaque matter under inquiry, affords to of brittle residue, according to the proportion of the two substances. I could not separate the supposed pus and mucus from one another, to exhibit them distinctly by water, or by any other means, on account, as I conceive, of the intimate diffusion through one another, and their mutual cohesion. But on evaporating the milky water, produced by agitating the sputum in it, or by letting it stand to collect the sediment, little else beside a mere congeries of globules seen under the microscope, was thus obtained. For the same reason, on standing, a serous liquid like that of pus (Sect. VII. 1,) does not separate, or only partially, from the opaque part, so as to render it possi ble by ablution, to collect this coagulable liquid like that of pus and the greater proportion of water, belonging to the mucus, occasions the coagulation by caloric, to afford only a milky liquid, instead of an uniform mass of curd.

:

This kind of sputum, consistently with the phenomena, must be produced by secretion from the bronchial membrane in its entire state, and not by ulceration or abscess. For it is secreted in many cases, at the rate of a pint or more in each 24 hours, for weeks and months successively, and for 20 or more successive winters. Also many persons recover their good health after this secretion, and it is the usual termination favourably of pneumonia, bronchitis, &c. It is produced by any disease of great irritation of the lungs; as I have found from ossification of the bronchial or pulmonary arte