FAT CELLS. 221 



body, and known as the adipose tissue. It forms a considerable 

 layer under the skin, constituting, along with the subcutaneous 

 areolar tissue in which it is lodged, what has been called the 

 panniculus adiposus. Around some internal parts it accumulates 

 for example, around the kidneys. It fills up the furrows on the 

 surface of the heart, and imbeds the nutritive blood-vessels of 

 that organ underneath its serous membrane. In several situa- 

 tions it lies beneath serous membranes, or is deposited between 

 folds of that tissue, as in the mesentery and omentum, there 

 affecting, at least in its first depositions, the course of the blood- 

 vessels. Tat also is observed around the joints lying on the 

 outer surface of the synovial membrane, or lodged, as it is in 

 the omenturn, in folds of that membrane, which project into 

 the cavity of the joint. It exists, moreover, in the bones, in 

 the interior of which it forms the marrow. As examples of 

 situations in which fat is not found during health, may be 

 mentioned the subcutaneous areolar tissue of the eyelids, the 

 lungs, and the cavity of the skull. 



Under the microscope the adipose tissue is found to be made 

 up of minute vesicles filled with an oily matter, and lodged, for 

 the most part, in the meshes of the areolar tissue. The vesicles 

 commonly cluster into little lobes, and these again collect into 

 the lumps of fat which become apparent to the naked eye. At 

 other times, as when they collect alongside the minute blood- 

 vessels of the membranous structures, the clustered arrange- 

 ment does not exist. The average size of the fat-cells is 

 from the 300th to the 600th of an inch in diameter. Each 

 consists of a very delicate envelope, transparent and homo- 

 geneous, enclosing what appears to be a single drop of oily 

 matter. 



It is the undue accumulation of the adipose tissue which 

 gives rise to obesity and polysarcia, from continually-increasing 

 quantities of connective tissue (areolar tissue) becoming in- 



