CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 771 



sido, ivmuins central though the collection uf fat has becoinr 

 considerable; it is however eventually displaced. The whole 

 process appears very similar to the deposition of mucin in the 

 cells of a mucous gland, 235 ; and we may by analogy infer 

 that the fat-cell becomes a fat-cell by the cell manufacturing fat 

 in some way or other, and depositing the fat so formed in the 

 interstices of its substance. The most striking superficial dis- 

 tinctions seem to be that in the mucous cell the granules or 

 spherules remain discrete within the cell, being separated by 

 bars of cell substance, whereas in the fat-cell the globules, as they 

 form, run together until at last they unite into a single mass ; and 

 further that while in the mucous cell, even when most heavily 

 loaded, a relatively large amount of active cell-substance still 

 remains, in the fat-cell a mere remnant is left and that chiefly 

 surrounding the displaced nucleus. 



Some observers are of opinion that the cells belonging to 

 connective tissue which thus become fat-cells of adipose tissue 

 belong exclusively to the kind which we spoke of as plasma cells, 

 105 ; but this is doubtful. Others again, while admitting that 

 the cells which become fat -cells resemble in appearance ordinary 

 connective tissue corpuscles and may like them be branched, 

 believe them nevertheless to constitute a special kind of connective 

 tissue corpuscle, being led to this view by the fact, that though 

 adipose tissue is very generally distributed throughout the con- 

 nective tissue of the body, it is apt to appear in particular 

 situations rather than in others, and in some tracts of connective 

 tissue never under normal circumstances makes its appearance. 

 Others again maintain that, under favourable circumstances, | 

 any connective corpuscle may become a fat-cell. 



The fat in the interior of bones forming the yellow marrow 

 appears to have the same general structure and to be formed in 

 the same way as the rest of the adipose tissue. 



504. The fat thus deposited in a fat-cell sooner or later 

 disappears. It is not ejected bodily into the surrounding lymph- 

 spaces of the connective tissue, but passes away either into the 

 blood stream or into the lymphatics by some processes not as yet 

 fully understood. The shell of cell-substance which forms the 

 envelope of the fat-cell is probably of a differentiated nature, and 

 may have properties which assist the escape of the fat ; but on 

 this point we have no exact knowledge. The disappearance of 

 the fat appears to take place in two different ways. On the one 

 hand, and this perhaps is the more ordinary method, the fat 

 gradually disappears, little by little, and the rounded distended 

 vesicle gradually assumes the characters of a connective tissue 

 corpuscle, even of a branched one. On the other hand, especially 

 when the disappearance is rapid and total, the space previously 

 occupied by fat becomes filled with a clear fluid resembling lymph, 

 the fat vesicle being transformed into a lymph vesicle. This 



492 



