430 E. T. Bell. 



fat cell. A mass of protoplasm containing small fat dr-jplets is shown. 

 No other thickening is present in the wall of this cell. A great many 

 cells of this type are present in this animal in the scrotal fat and in 

 various portions of the subcutaneous fat. Many of the cells show 

 more than one thickening in the wall caused by small accumulations 

 of protoplasm. Similar small masses of protoplasm containing small 

 fat droplets were found in cells of all sizes up to 125 microns, but 

 the protoplasm is present less frequently and in smaller amount in 

 the larger cells. The same kind of fat cells were found in large 

 numbers in corresponding portions of the adipose tissues of several 

 other fat steers. These cells are clearly similar to the cells of the 

 full-term foetus (Text Fig. 10). They are j^robably merely young fat 

 cells. High magnification reveals the presence of some very small 



m 



Text Figitre 11. Thickened part of wall of fat cell from a fat steer. A 

 great many cells in the animal are of this type, f, spaces occupied by small 

 fat droplets ; F. position of main mass of fat ; fir, Altmann granules ; m. cell 

 membrane; ». nucleus. Fixation, 20 per cent formalin. Stained with iron- 

 h;em. X ^'<'- 



masses of protoplasm immediately under the cell membrane in 

 many large fat cells, but the protoplasm does not form a continuous 

 layer. 



The cell membrane is differentiated from the peripheral proto- 

 plasmic layer of the cell. It begins to develop when the cell is yet 

 branched (Text Fig. 7, B and C ; Text Fig. 8, A and B). It develops 

 only a short distance on the cell processes. The membrane increases 

 in thickness as the cell grows. It has long been known that the 

 cell membrane is different chemically from the protoplasm and con- 

 nective tissue fibers. It is not stained by Mallory's anilin blue^'* 



"If the tissue be flxed in formalin, anilin blue will stain the membrane 

 of the fat cell. 



