The term Bright's disease is here limited to Simple inflammations of the Kidneys, whether acute or chronic, which are bi-lateral, and hence due to conditions of the blood. The inflammation does not occur around definite centres, and seems, therefore, to be due to substances in solution acting on the kidney tissue. The term is thus synonymous with Nephritis, but excluding those forms of inflammation, such as septic which are due to the local action of microbes.
The irritant dissolved in the blood, as just mentioned, acts on both kidneys and on all parts of the organs. But, as the cortex contains the more active secreting tissue of the organ, arid as the blood is primarily distributed to it, we find that the inflammatory manifestations occur chiefly in that region. Again in the various cases of Bright's disease we do not find the different constituents of the kidney tissue equally engaged. An irritant brought to the kidneys by the blood may show a predilection for the renal epithelium on the one hand, or the connective tissue on the other. It may be said, indeed, that for the most part irritants which act through a long period and with little-intensity produce a chronic inflammation mainly affecting the connee-tive tissue. On the other hand, irritants which act intensely so as to produce acute inflammation, while they induce the usual changes in the blood-vessels which we have seen to occur in acute inflammations, affect mainly the glomeruli and the epithelium of the uriniferous tubules. It may therefore be said that acute inflammations are mostly Parenchymatous, while chronic inflammations are mostly Interstitial.
As to the Nature of the irritant there are some forms in which the specific poison of an infective disease is the agent. Thus Acute Bright's disease is a frequent sequela of Scarlet fever, and more rarely of measles and other acute fevers. This would indicate that in other cases of acute nephritis an organic poison is the probable cause.
No such agent can be definitely distinguished in a large proportion of cases. The disease is often ascribed to Cold. In this connection Dickinson points out that cold mostly produces nephritis when the person is exhausted or asleep, or when the exposure has occurred immediately after profuse perspiration. It is as if, the functions of the skin being suspended, some deleterious material had accumulated in the blood and irritated the kidneys. It appears that nephritis hardly occurs in persons exposed to cold in the Arctic regions, probably because, the respiration being more vigorous, the deleterious material is carried off by the lungs. In warm climates also nephritis is uncommon, probably because the body is less liable to sudden exposure to cold than in temperate regions.
As to the nature of the irritant in Chronic Bright's disease we have in Gout an irritant which is known to produce inflammation in other parts besides the kidneys. The pathology of gout is not very apparent, but there is an obvious alteration in the blood in consequence of which salts of uric acid are deposited in certain joints, generally with signs of acute inflammation. The same condition of the blood frequently induces chronic nephritis, and it is remarkable that when it attacks the kidneys it is less likely to affect the joints, and vice versa. Among the working classes gout largely arises from chronic Lead-poisoning (see statistics in Dickinson's work on Albuminuria), and in these cases the disease is particularly liable to attack the kidney, so much so that a large proportion of painters and others who work with lead die of chronic nephritis. Where the gout is due to the constant use of alcohol the disease is more liable to attack the joints. Chronic nephritis is also sometimes induced by the poison of Syphilis. In this case it is apt to be associated with amyloid disease, but may also occur as a simple inflammation.
Pregnancy not infrequently leads to a chronic nephritis, in all probability by obstructing the vessels of the kidney by the pressure of the uterus. In recent cases there is extreme hyperemia of the kidney, which, with repetition of the cause, may go on to assume the regular characters of chronic nephritis.
Lastly, there are cases in which there is no special cause apparent, and we can only say that the person has been exposed to some influence whose nature we do not know. In many cases the disease has been very prolonged, and, all through, the actual active disease at any particular time has been very slight. With this very insidious march, there may be the most serious permanent changes in the kidneys before any prominent symptoms have called attention to these organs.