LIPOID CONTENT OF THE KIDNEY TUBULE 71 
of mitochondria. Mitochondria are soluble, wholly or partially 
in fat solvents, alcohol, ether, chloroform, and dilute acetic acid, 
and the part which is not soluble is a protein (albumin?). They 
are rendered insoluble by chromation. Mitochondria do not 
stain with sudan III or scarlet red and are blackened only at 
times with osmic acid. Because of their lipoid nature, some 
have sought to find in them the source of lipoids in the cell, while 
others believe they themselves arise from lipoids (Cowdry, 716). 
The problem of the source of visible lipoids in tissues is one 
that has aroused much interest and has been very much involved 
in the questions of fatty infiltration and fatty degeneration. 
One explanation that visible ‘fat’ is due to the coarsening of a 
fine emulsion of lipoid has already been given. Others believe 
that fatty infiltration is an excessive deposition of fat and that 
fatty degeneration is a conversion of cell substance into fat. 
(Virchow from Fischer and Hooker). E. T. Bell (14—’15) refers 
to two divergent opinions on this subject in his paper on ‘“The 
Differential Staining of Fats.” Rosenfeld (’04) and Kraus (’03) 
believe that kidney fat is derived mainly from the destruction of 
intracellular lipoids or from structural changes in the cytoplasm 
whereby finely divided fat becomes visible. Ribbert (’03) says 
that lipoids are mainly extracellular in origin and that the origin 
of intracellular lipoids ‘is comparatively unimportant. Bell 
suggests that oleic fat is extracellular in origin and other lipoids 
are intracellular. From this brief account of the problem of 
lipoids in tissues, it can be readily seen that the question is one 
of importance, and the significance of the presence of lipoids 
will be taken up in the general discussion at the end of the paper. 
Just as it has been brought out in the first part of the intro- 
duction that tissues possess lipoids, which are difficult in general 
to demonstrate microscopically, so is it true concerning the lipoid 
content of the kidney. Krauss, in 1904, makes the statement, 
“that tissues that are microscopically fat free, and look normal 
in general, for example, kidney cells, may contain 20 per cent of 
fat.” As late as 1909-1910, Mayer and Rathery state that no 
fat disclosed by usual reactions is found in the kidney cells of 
mammals. 
