RESULTS OF FIXED TISSUE STUDIES 119 



The picture of the mitochondrial structure of the other tubular' seg- 

 ments corresponds in general to those described for the normal with cer- 

 tain small variations under ordinary conditions. The glomeruli and their 

 capsules are practically free from mitochondria in the kidney under normal 

 activity, and urea feeding does not bring on an increase (see Figs. 15 and 

 16). There are no indications anywhere in the tissues that pathological 

 changes had been produced by urea feeding. 



A number of observers have ascribed a secretory role to the mito- 

 chondria of the kidney, such conclusion being based on animal experi- 

 mentation. For instance, during hibernation Ferrata(34), Disse(35), and 

 Monti (36) found the following changes from the normal under ordinary 

 circumstances : the lumina of the convoluted tubules are narrow and the 

 epithelium is not sharply outlined but markedly granular. Near the base 

 the granules assume a regular chainlike arrangement, while the inner and 

 less dense part of the cell is traversed by fine threads. When secretion 

 sets in, this latter part of the cell becomes quite transparent, bulges toward 

 the lumen and granules replace the threads. This appearance was con- 

 sidered a storage of granules supposedly characteristic for a prophase of 

 secretion. 



Also Takaki(18), working with starvation and dry feeding, and 

 Kolster(6), using similar methods together with sodium chloride injec- 

 tions, concluded that mitochondria have a definite place in the secretory 

 process of the kidney. Their investigations tend to divide the stages of 

 secretion according to the appearance and arrangement of mitochondria. 

 Their findings have been confirmed by Schultze(37). It is of greatest 

 importance that Regaud(38), after most exhaustive studies, concluded 

 that all the various types of granules, rods, and filaments described under 

 different names belong to the same group, namely, mitochondria, and that 

 they varied in their appearance according to a number of conditions 

 among which were changes in the secretory activity of the cell. It was 

 Simon (39), Retterer(40), and Henschen(41), and to some degree 

 Dumas(42), Mayer and Rathery (43), who substantiated Regaud's con- 

 clusion by further experimental work. Nevertheless, the changes men- 

 tioned have been thought to be artefacts by Prenant(44), Policard(45), 

 Levi(46), and Ciaccio(47). 



I cannot agree with the latter, since I feel certain that the mito- 

 chondrial play seen in these studies, and of which photomicrographs are 

 presented here, is not the result of variations in fixation. It is true that 

 different fixations (fixing agents) of pieces from the same tissue will show 

 slight differences in the appearance of the individual mitochondrial unit, 

 but aside from this the variations observed within one piece are constant 

 for that fixation, and correspond to the variations in pieces fixed differ- 



