Causation. Chronic nephritis is the common sequel to the acute forms, whatever their origin, but it may also occur primarily from repeated chills produced by such conditions as exposure to heavy continued rain when at grass, chills contracted during cold nights and the great variations in temperature in spring and autumn. The conditions, however, thus produced are rather of the nature of subacute nephritis than of chronic nephritis, properly so called.
These forms of chronic nephritis may also occur primarily in consequence of chronic hepatic lesions with pressure on the posterior vena cava, producing blood stasis in the kidneys. Finally, they may represent the delayed effects of slight lesions which have escaped notice and have developed during grave diseases or as a consequence of repeated gestation.
From the anatomico-pathological standpoint, the only conditions hitherto recognised are the chronic hypertrophic forms of nephritis (large, white sclerotic kidney with lardaceous degeneration and sometimes marbling). This is probably because the animals are slaughtered as soon as they suffer in condition, but if they were kept long enough they would undoubtedly suffer also from the atrophic chronic forms of nephritis found in man and in the dog. In the case of man observation has shown that these two forms only represent different stages in the development of one disease, the large, hypertrophied kidney of the early stages afterwards undergoing marked progressive atrophy.
The symptoms are at first so vague that diagnosis would be impossible on a single examination. Seuffert states that the condition develops as follows:—
The first sign, loss of appetite, is soon followed by constipation and dull colic, due to congestion of the kidney; the pain is often so great as to cause intermittent groaning.
The urine passed is always turbid, and sometimes blood-stained, but this staining rarely lasts longer than a week. The urine then gradually resumes its normal appearance, is passed in small quantities, and contains more or less albumen. The yield of milk markedly and progressively diminishes.
If treatment is resorted to at this stage laxatives and diuretics appear to effect a real improvement. Unfortunately, however, the apparent improvement is but temporary; the kidneys become hypertrophied, and the right soon occupies the whole of the sublumbar space, its margin extending as far as the extremity of the transverse processes near the anterior angle of the hollow of the flank.
This hypertrophy and the extreme sensitiveness can be detected by external palpation. Internal examination confirms the facts so observed as regards both the kidneys.
The patients eat little and become thin, whatever treatment be adopted. They progressively waste, and die after some months in a state of marasmus, exhausted and intoxicated.
It is very probable that the digestive disturbances are complicated by respiratory and cardiac trouble, as in man and the dog; but neither cardiac nor uræmic disease of the kidney has been recorded.