RESULTS OF VITAL STAINING STUDIES 113 



the influence of foreign substances. It did occur to me that by polariza- 

 tion such a question could be settled. Unfortunately, at the time of this 

 investigation this chance was overlooked. 



The only result in this part of the investigation that can be oflfered 

 as a fact is, that in Janus green studies the tubules which were proven 

 by Leschke(12) and Oliver (13) to give off urea also are the ones that 

 have the greatest abundance of mitochondria, and that the tubules which 

 Suzuki (14) considered the resorption tubules, have no or very little mito- 

 chondrial structure. But that there is a difference in vital staining reac- 

 tion between the mitochondria of kidneys after long-continued or acute 

 strain in urea excretion, as compared with those acting normally, cannot 

 be asserted. 



Since in some of the first tissues studied vitally there were seen 

 spherical, highly refractile bodies of various sizes apart from mitochon- 

 dria, Sudan III and scarlet r. were employed in the remaining tissues 

 after a Janus green penetration had been obtained. These round bodies 

 stained brilliantly and instantaneously with the so-called fat dyes which 

 did not influence the green-stained mitochondria. The arrangement of 

 these bodies was irregular and without any apparent similarity in neigh- 

 boring cells in the entire group of tissues studied. That is to say, they 

 were as numerous in the controls as in the urea-fed rats of the first and 

 second group. From this I judge that normally there is free fat, or a 

 substance related to fat, in the cells of the kidney of white rats. At no 

 time did these round bodies stain with Janus green, and this dye is specific 

 for mitochondria. It is obvious that these bodies are not aberrant physi- 

 cal forms of mitochondria. In the fixed sections similar, or perhaps the 

 same, structures have been seen by several investigators, and explanations 

 have been offered which point out that these bodies may be concerned 

 with secretion. Heidenhain(25), Hoeber and Koenigsberg(26), \'an der 

 S'tricht(27), and Gurwitsch(28) have described intracellular vacuoles of 

 various positions and sizes. These vacuoles were thought to act as collec- 

 tors of secretory materials. Gross(29) and Hirsch(30) were not able to 

 confirm the presence of these vacuoles. Retzius(31) observed these struc- 

 tures but did not think them vacuoles. He rather interpreted them as true 

 droplets of secretion. In these droplets he saw very fine granules con- 

 nected by fine threads. At a time when the cell appeared high and the 

 brush border had disappeared these droplets were supposed to be expelled 

 into the lumen of the tubule. 



In my fixed sections the position and sizes of the occasional "vacu- 

 oles" observed seemed to correspond in location to the fat bodies de- 

 scribed above. At no time could I find sufficient proof that in the vitally 

 stained tissues fat droplets were similar in arrangement or staining to 

 mitochondria. Nevertheless, it may be possible that these substances are 



