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RUTH RAND ATTERBURY 
Thus two zones are usually distinguished in the metanephrogenic 
strand, an inner and an outer zone. The secretory cells of the 
nephric tubules are believed to arise from the inner zone, the 
stroma cells, from the outer zone. The cells of both zones are 
mesenchymal in character, and in the early stages of develop¬ 
ment essentially similar in structure. A difference in density 
of the tissue seems to be the only morphological distinction 
between these zones. 
The mesenchyme-like tissue of the kidney anlage, abundant 
in early stages of development, diminishes gradually in amount 
with the specific differentiation of the nephric tubules. In 
later stages of development, as well as in the adult kidney, the 
stroma consists of sparse, apparently inert, connective-tissue 
cells scattered among the renal tubules and about the blood 
vessels. Under pathological conditions this tissue in man may 
proliferate intensively (nephritis interstitialis). The appearance 
of bone, bone-marrow, and blood formation following special 
experimental conditions has been described in the kidney of the 
adult rabbit by Sacerdotti and Frattin (’02), by Poscharissky 
(’05), and Maximov (’07). The formation of bone and bone- 
marrow was interpreted by these authors as a local metaplasia 
of the connective-tissue cells of the stroma. According to 
Maximov, however, the blood formation observed in these 
experiments is to be interpreted as a local proliferation of young 
blood cells brought into the kidney from other hemopoietic 
centers by way of the blood current. In the opinion of Maximov, 
no one can seriously entertain a belief in the possibility of hemo¬ 
poietic potency in the scanty connective tissue of the adult 
kidney. 
Only in lower forms is the kidney regularly a seat of hemo¬ 
poiesis—the mesonephros of fishes being a permanent organ of 
blood formation. The meso- and metanephros of birds and 
mammals never display hemopoietic activity either in embryonic 
development or in the normal adult condition. However, it 
was shown by Danchakoff that in chick embryos the stroma of 
both the meso- and metanephros possesses hemopoietic potency, 
although under normal conditions this is not revealed. A marked 
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