I. In the first series of observations on seven adult rats fed on a horse-flesh diet for five months, the kidneys show very striking histological changes, when compared with the kidneys of the control animals fed on porridge and on bread and milk. These pathological changes conform in type to what is seen in the kidney in general toxic conditions, e.g., septicaemia, diphtheria, acute lobar pneumonia, etc., the chief incidence of the affection being on the cells of the secreting tubules. While the kidneys of this series show uniformity as regards the type of lesion (catarrhal nephritis), they show variations in degree. The majority of the kidneys of this series are examples of a severe type with bacteria present in large numbers.
In the less affected cases, the earliest changes are always found in the ascending limb of Henle's loop, which appears to be the most vulnerable of the secreting tubules. It is noteworthy that in sections where the cells of the convoluted tubules in the cortex may show little change beyond swelling and increased granularity of their cytoplasm accompanied by karyolytic changes, the cells of the ascending limb of Henle may have already undergone an advanced degree of disintegration; a pyknotic condition of the nuclei and subsequent karyorhexis being very striking and constant associated phenomena.
In the kidneys which are more gravely affected, the convoluted tubules in the cortex are affected equally with the ascending limb of Henle, and while some of the convoluted tubules show disintegration of their cells (especially the tubules immediately subjacent to the capsule), in others the change is more of the nature of a coagulation necrosis. The collecting tubules are for the most part normal, but in the more severe cases many of the smaller collecting tubules in the cortex and medulla contain colloid casts, which have been formed by the fusion of necrosed secreting cells.
The other structures of the kidney are affected to a much less extent than the secreting tubules. The glomerular capillaries show a varying degree of congestion; in the severer cases the capillary walls are the seat of an acute hyaline swelling. The interstitial tissue shows some degree of cedema and congestion of the intertubular capillaries, but no sclerosis.
II. In the second series of observations on five castrated female rats fed on a horse-flesh diet for four or live months, the kidneys of two of the five animals show no differences in structure from those of the control subjects. In the remaining three the kidneys show an early catarrhal nephritis, the lesion being most marked in the ascending limb of Henle's loop. The vessels appeal normal, and there is no indication of interstitial change.
III. In the third series of observations on young animals fed on ox-flesh or horse-flesh, the kidneys of the ox-flesh-fed animals are practically normal. In the three rats which were fed on horse-flesh for eight months the appearances are abnormal, the changes being of the same nature as those described in the first series, but much less in degree. In two of this series there are isolated accumulations of cells of the lymphocyte type along the lines of the interlobular vessels.
IV. In the series of observations on the second generation of meat-fed animals, the kidneys of the majority show no pathological change. A small minority in this series show changes corresponding to an early catarrhal nephritis. In one litter of three animals (b, Table IV.) which were killed when three months old, the kidneys present a perfectly normal appearance.
V. In the series of four animals which were fed on ox-flesh for nine months, the diet being commenced when the animals were about three months old, the kidneys appear normal.
The application of Muir's hsematoxylin-eosin stain to the kidneys of the meat-fed subjects which appeared normal by ordinary staining methods, shows a striking alteration in the granules of the secreting cells. The changes may be briefly described as -
1. An irregular distribution of granules throughout the secreting cells, the granules not being confined to the base of the cell as in normal kidneys. Many granules may also be present in the lumen (see Plate).
2. An alteration in the size and staining affinity of the granules, the granules being much larger in size and taking a deeper stain. The nuclei of the secreting cells are also more deeply stained (see Plate).
In the kidneys which show catarrhal changes the granules are very few in number, or may be absent.
To gain an idea of the conditions of some of the animals as regards nitrogen metabolism, the following experiments were made: -
The adult rats, which for some time had been maintaining nearly the same weight, were isolated in specially constructed cages. These cages allowed of the collection of urine and faeces from day to day. (To prevent the loss of urinary nitrogen as ammonia, a few cubic centimetres of dilute sulphuric acid were placed in each receptacle.) The output of N in each case was then determined by submitting all the feces and an aliquot part of the urine to the process of Kjeldahl. The intake was calculated from the total amount of food consumed (from a specially conducted analysis of each diet).
Two of the rats were on ox-flesh (with writer ad libitum), which had been their exclusive diet for four months previously; one was on the standard diet (bread soaked with skimmed milk). The figures represent the intake and output for a period of four days. The weight of the animal and the total weight of food which it consumed, are also given.
Bread and Milk.
Weight of animal ....
Food consumed ....
Intake of N.....
Output of N
It appears from this table -
1. That all the animals were practically in nitrogenous equilibrium.
2. That the quantity of food taken was such as to render the amount of nitrogen metabolism per unit of body-weight the same, quite irrespective of the nature of the diet provided. Thus, taking the average of intake and output to represent the nitrogen metabolised, we get for each kilogram of body-weight the following figures (for four days): -