102 THE MICROSCOPE. 
peripherally situated nucleus and body distended with fat. In a 
cross section of one of the processes of a fat body taken from a frog 
in the early spring, the special plasma cells, from which the fat cells 
are to be formed, together with the partially formed cells, are found 
in greatest number at and near the periphery of the section ; the 
more mature cells, whose bodies are filled with fat, occupying mainly 
the central portion. 
The special plasma cells (primordial fat cells) bear no resem- 
blance (other than a general one) to connective tissue cells, and 
there is no evidence, to be adduced from observations on the cells of 
the fat bodies of the frog, tending to show that the fat cells of these 
bodies ever arise from the cells of connective tissue. 
On the contrary, it is seen that the cell ordinarily known as the 
fat cell is but the secondary and mature form of a special cell. 
This special cell in its primary form is oblong in shape, with a dis- 
tinct nucleus and intra-nuclear reticulum well marked. (Fig 2.) 
This reticulum has the form of the rosette in karyokinesis, but 
whether or not it is a step in this process I cannot positively say, as 
I have been unable to make out other karyokinetic figures either 
preceding or following this one. That it is one of the phases of 
karyokinesis is rendered very probable by the nuclear division which 
follows ; and it is doubtless owing only to insufficient refinement of 
technique that the entire process has not been observed. However, 
this is, as regards the purpose of this article, of secondary importance, 
as it is the peculiar change undergone by the cell and its nucleus, 
during the passage of the cell into its second stage, to which I par- 
ticularly desire to call attention. 
This change, of which the formation and deposit of fat isa 
part, differs markedly from anything I have myself observed in 
other animals, or seen recorded as occurring during the development 
of the adipose cell in them. The fat cell is described by various 
observers as developing either from a connective tissue cell,* or 
from a special plasma cell,y or from either,{ by the formation of 
minute drops of fat in the body of the cell, the drops increasing in 
size and coalescing into one, which continuing to grow, distends 
the cell until it is but a protoplasmic envelope of the contained fat. 
* The authorities who hold the connective tissue origin of fat cells are: Quain, Frey, 
Virchow, Klein, Klein and Smith, Flemming, Von Wittich, Prudden. 
+ The supporters of the special plasma cell origin of the fat cell are: Ranvier, 
Hoggan, Rollett, Czajewicz. 
¢ Professor Gage from observations on the Necturus, concludes that the fat cell may 
arise from either connective tissue, or special plasma cells. See his article: ‘‘Observations 
on the Fat Cells and Connective Tissue Corpuscles of Necturus (Menobranchus)’ ‘‘Pro- 
ceedings of the American Society of Microscopists,”’ 1882, E)mira Meeting; which also con- 
tains an extensive bibliography. 
