held fluid by excess of carbonate of ammonia, and gently evaporated down, may be brought to have all the characters of cholera blood. Thus reduced, it may be again made fluid by addition of the water lost, and may be induced, by displacement of the alkali, to coagulate firmly.

In cases where the blood is surcharged with alkali, and where the water is not deficient, cases of fever par excellence, the fibrin, held in too permanent solution by the blood-stream, is infiltrated into the structures of vascular organs. If the blood here congested remain locked up, a condition obtains somewhat similar to what occurs in the blood enclosed in the vessels after death. The alkaline solvent is gradually eliminated into the surrounding structures, and the fibrin is at length deposited or stranded in the infiltrated part. Thus deposited, it forms those semi-plastic exudations SO common in many diseases of a low or asthenic inflammatory fever type; ultimately, if recovery takes place, it either undergoes transformation and becomes the basis of a morbid growth, or remains a firm fibrinous exudation, the more fluid parts of the liquor sanguinis, with which it was originally in company, being removed by absorption.

But while the considerations above noted lead to an explanation of many symptoms and pathological states commonly met with and recognized, they invite also to work at deeper strata. They are secondary to and dependent on the development of the agent which in excess produces them.

If we may allow ourselves to take a broad view of pathology, symptomatological as well as anatomical, we may look on every pathological state as a modified physiological process.

There is not, on strict scrutiny, a single feature in disease which does not bear such interpretation. What therefore leads to the normal development of the alkaline solvent of the blood, may lead in extreme instances to its development in excess. This recalls us to a physiological problem yet unsolved. But it is not in every case necessary to trace back the primary cause to its primary source.

By this I mean that there are conditions which may lead to derangements of the body from superalkalinity of blood, independently of the idea of the production of the alkali in excess by an exaltation of the physiological process by which it is normally produced. As a first example, there are external sources. In health, the blood is capable of absorbing but very limited quantities of ammonia by the lungs. We have seen an explanation of this fact in speaking of the rapid elimination of the alkali from drawn blood: i. e. there is, in the fixed alkaline property of the blood, as well as in the temperature of the blood, an admirable provision against excessive absorption. For, were ammonia capable of absorption by the blood as it is by water, there is not a foul place where decomposing organic matter delivers up its ammoniacal emanations, which would not be at once and permanently a very plague spot, the heart and home of fever, absolutely uninhabitable. I do not question, however, that an ammoniated air constantly inhaled is and must be injurious, despite the provision made for its exclusion. There may, moreover, be conditions of blood, otherwise brought about, such as an excess of water, which favour the absorption of the alkali, and may be accepted as so-called "predisposing causes (a term often violently abused,) for the re

ception of the alkali; and thus symptoms of disease may arise from simple exposure to the alkaline vapour. But these instances are rare; and the symptoms produced are either transient when they are lighted up, or, if permanent, slow and feebly defined.

In a close room, through which ammonia vapour is diffused so widely as not to be detectable by the sense, I know from personal experiment that the air thus feebly charged is for a time the cause of symptoms, to say the least of them, disagreeable. There are headache, nausea, giddiness, and debility. These symptoms pass away as fresh air is breathed; but, by frequent repetition, they at length produce a more permanent debilitating influence.

Hence I presume that much of the excitable anæmic feverish state, to which persons who live in foul localities are subjected, may have its origin in the cause thus specified. We must push this argument but little closer now; for that fever is ever actually lighted up in such way, there is as yet no satisfactory proof. But that fever once lighted up would find its course and its intensity favoured by the inhalation of an air bearing even one ten-thousandth part of ammonia, is an inference fairly derivable from the labours which have gone before.

But the matter here considered must not be left without a word of suggestion. Brooding in low and filthy localities, there is common to them a form of fever, endemic in its character, doubtfully contagious, and seeming to want habitat only to take form and live.

While some experimentalists occupy themselves in seeking in organic cells for the cause of this disease, others might, with equal chance of success, and with more precision, look for it in one of that numerous

family of volatile alkaline principles, coming from the death of the organic world, of which the common ammonia forms but a single representative.

Wherever there is an air containing such a trace of fœtid vapour as to be detectable by the senses, and often when the senses fail to detect it, there ammonia exists in one or other of its varieties.

The microscope test is invaluable in such researches, since all the ammonias yield characteristic crystals of the chloride. Another delicate test for ammonia is the iodized paper for ozone; the merest trace of ammoniacal gas, such as would be inappreciable under ordinary circumstances, being a sufficient check on the action of the ozonometer.

In tobacco-smoke, an ammonia is given off in large quantities. If a microscope glass moistened with hydrochloric acid be held for but a moment over the fume of the weed, and be then dried, the glass will be found frosted with crystals of the chloride of ammonium.

The breath of all confirmed smokers is markedly ammoniacal; and I have shown in experiment XVI, p. 101, what the effects of inveterate smoking are on the blood. There is no doubt that some ammonia is absorbed from the pipe in prolonged smoking; the modification of the blood-corpuscles and the fluidity of the blood incident on prolonged inhalation of the tobacco fumes proclaim the fact; while part of the prostration, the anæmia, the nausea, and the hysteria to which great smokers who have not the lungs of Stentor, are subject, are possibly traceable to superalkinity of blood, and to tobacco as the source of the alkali.

In cases where the function of the kidney has been suppressed, we have a fair insight into the origin of

the ammonia salt with which the body is poisoned from the excess of the ammonia. We find the source here in the non-elimination and subsequent decomposition of the urea. In experiments where the kidney is extirpated, this superammoniacal state of the blood prevails. The blood is rendered fluid, the corpuscles are dissolved, and coagulation can only be induced by the addition of caustic lime, or the cautious addition of potassa or soda, so as to secure the elimination of the ammonia. The breath also before death is strongly ammoniacal. In fatal cases of scarlet fever, where the function of the kidney as well as that of the skin is suppressed, the fœtid breath is loaded with the alkaline excreta, and the convulsions and coma are accounted for by a simple toxical cause. The same argument might extend to many other diseases, preceded in their later stages by an arrest in the action of the two great emunctories, the skin and the kidney.

During periods when the body is exhausted by over fatigue, and especially when to this prolonged abstinence is superadded, the excess of ammonia evolved by the breath is well marked; and impoverishment from imperfect diet is in itself a cause of diseases marked by great fluidity of blood, exudations, and flux. In these cases, the breath is alkaline, and the blood-corpuscles are more or less dissolved. The excreted matters thrown off by the stomach and bowels are fœtid and charged with ammoniacal compounds; while the symptoms, the convulsions, and ultimate coma, are in a general sense identical with those of slow alkaline poisoning. In short, when the balance between the forces of regeneration and decay is broken, and the former kicks the beam, there is set up a decomposition,