432 E. T. Bell. 



inside the lobule. Text Fig. 12 represents a lobule of renal adipose 

 tissue from a 40 cm. foetus, under a low magnification. A number 

 of nuclei in the lobule stain intensely with hsematoxjlin and are prob- 

 ably in some stage of division. Two mitotic figures (m) are shown. 

 Fig. 10, Plate II, shows clearly these, young fat cells among the older 

 cells. Probably only a few of these young cells Were developed directly 

 from the original branched cells of the preadipose tissue. They arise 

 by the division of fat-free cells inside the lobule. 



In almost any section of adipose tissue a few nuclei may be seen 

 crowded in the angles between the fat cells. The protoplasm around 

 these nuclei is so small in amount that it can hardly be demonstrated. 

 From a study of fattening animals I am convinced that these in- 

 terstitial cells may form many new fat cells when the animal fat- 

 tens. I have not, . however, found mitoses in the interstitial nuclei. 

 It is generally believed that a cell does not divide after any consid- 

 erable amount of fat has been deposited in it. 



A great part of the growth of the fat lobule is certainly due to 

 the increase in size of the individual fat cells. A cell increasing 

 its diameter from 15 to 150 microns (the latter being a common size 

 in fat cattle) increases its cross-sectional area 100 times and its 

 volume 1,000 times. The subcutaneous fat cells of thin cattle are 

 markedly smaller than those of fat cattle. The increase in the volume 

 of the fat cells already present is sufiicient to account for a large 

 part of the increase in the mass of the adipose tissue during fatten- 

 ing, but a numerical increase of the fat-holding cells also occurs. 



As pointed out above, fat cells with a peripheral protoplasmic 

 margin containing small fat droplets (Text Fig. 11) were found 

 in large numbers in the subcutaneous adipose tissue of several fat- 

 tening steers. This type of cell is usually comparatively small, and 

 is essentially identical with the fat cells of the foetus. (Text Fig. 

 10 and Fig, 10, Plate II.) They are very probably newly-formed 

 fat cells developed from the interstitial cells referred to above. 



During the fattening of the animal it is evident that some new 

 fat lobules are formed around old or newly-formed blood vessels. 



It can no longer be maintained that the fat cell is a special kind 

 of cell in the sense used by Toldt, distinctly different from the ordi- 



