different noxious effluvia can exert their full action on the fyftem without being taken into the mafs of blood; there is no neceffity, therefore, for fuppofing infectious miafmata to be abforbed. They may act on the brain through the medium of the mouth, noftrils, lungs, ftomach, or skin, with all of which they must come in contact. Whether they actually do fo in all cafes, or in any, or whether they are in fome inftances abforbed, and carried into the fyftem, it is difficult to determine; but in either case their action is probably exerted on the fentient extremities of nerves; in the latter cafe, on those distributed on the internal coats of the blood-veffels; in the former, on those of the general surface of the body, or of the cavities which open externally.

In the application of certain infectious, matters to the body, as of the variolous or fyphilitic virus, we are apt to imagine that we can trace the progrefs of the poifon into the fyftem step by step. First, no effect is perceived for feveral days; then the punctured part becomes inflamed, and the inflammation can be often traced along the courfe of the abforbent veffels to the next lymphatic gland, which itself becomes enlarged and

painful, as if acted upon by the presence of a foreign ftimulus; and, after all this, follows the conftitutional affection, Hence we are accustomed to confider the absorption of the poifon in these cafes as almost a matter of demonftration. This conclufion, however, upon attentive confideration, will scarcely be found to be warranted,

In the first place, the fame phenomena fometimes present themfelves, where no peculiar matter has been applied; as when the fkin is punctured by a thorn, or a clean polished inftrument, as a needle or the like, The induration of the lymphatics, and of the gland above, can only be afcribed in this cafe to the communication of inflammation through a series of parts of fimilar organization and function; circumftances which we know, from general obfervation, to be the foundation of an intimate fympathy between different and diftant parts.

In the next place, upon the principle of abforption, it is difficult to account for the poifon lying fo long a time in the part to which it is at firft applied, and for this time being fo unequal with regard to different poifons:-a fresh wound is known to be a good abforbing furface with re

to

gard to other applications. Nor does the idea of abforption at all enable us to underftand various other circumftanees attend

ing infection. It does not explain the ftrongly-marked difference between the cafual and inoculated fmall-pox; nor the limited action of the variolous and other poisons in the system. If absorption of these poisons were neceffary in order to their action, the general diffusion which they must neceffarily undergo might be expected to produce a more general effect than is actually obferved. Quantity, likewife, might be fupposed to influence the event; which, however, does not seem to be the cafe,

What has been just stated I do not by any means confider as proving inconteftibly that contagious matters are not abforbed previous to their acting on the general fyftem; it only ferves to fhew, that the contrary has been affumed rather than demonftrated; and, therefore, that we ought to be cautious in employing it as a basis of future reafoning, particularly in regard to the treatment of diseases.

Sect. V.---Of the Alternation of Fever with Inflammation.

FEVER is frequently obferved to alternate with inflammation; and as one inflammation is often removed by the acceffion of another, fo fever and inflammation in many cafes prove reciprocally a remedy for each other. Thus in eryfipelas, and other external inflammations, metaftafis, as it is called, not unfrequently takes place to the brain, and idiopathic fever enfues; and, on the other hand, fever is fometimes terminated critically, in confequence of inflammation arifing in fome external part of the body.

Both fever and inflammation often go off spontaneously upon hæmorrhage, diarrhoea, or other critical difcharges, taking place. They agree, likewife, in this refpect, that, when once excited, they are both in a great measure independent of the cause which first produced them, and continue their progress according to certain laws of the œconomy, with fimilar tendencies to terminate at some certain periods, rather than