CONNECTIVE CELLS. 



45 



cells as are drawn in Fig. 46. Their protoplasm contains a number of 

 large vacuoles and the nucleus is sometimes central. Such cells may be 

 found in subcutaneous tissue, but are more often seen in the omentum 

 or around the kidneys. In extreme emaciation the fat cells become 

 flattened and several small vacuoles replace the one large one. These 

 cells are said to produce a mucoid substance appearing both between and 

 in the cells. 



Fat cells develop in the fetus in lobular groups around small blood vessels. 

 They are always found under the skin, behind the eye and in other definite places, 

 so that they have been regarded as secretory organs. Like gland cells they take 

 material from the vessels near by, either fat which is stored with but little change 

 or sugar and probably albuminoid bodies which are transformed into fat by the 

 activities of the cell. The process has been said to begin in or near the nucleus 

 with the formation of granules, which disappear as the vacuoles develop around 

 them. ' The small vacuoles in the nucleus have been 

 described as containing an alkaline fluid which is 

 not fat, and which is discharged into the proto- 

 plasm. They are also described as fat droplets and 

 are observed in cells full of fat rather than in those 

 beginning its formation. Like an internal secre- 

 tion, fat is taken from the cells into the vessels, 

 though probably not in the form in which it is 

 stored. It should be remembered, however, that 

 most cells take material from the blood and trans- 

 form it into new substances. They also very gen- 

 erally may effect the body by the products of their 

 activity. Unless the term "gland cell" is to be so 

 extended as to lose its significance, lobules of fat 

 should not be considered glands. 



FIG. 47. FAT CELLS FROM THE 

 AXILLA OP AN EXTREMELY 

 EMACIATED INDIVIDUAL. 

 X 240. 



k, Nucleus; f, fat droplets; c, cap- 

 illary blood vessels; b, connec- 

 tive tissue. 



Besides the mesenchymal cells which early 

 become differentiated into fat cells, the cells of 

 adult connective tissue, of cartilage, and the 



epithelium of the liver all form fat vacuoles which may or may not coalesce. 

 Pathologically fat appears in many kinds of cells, sometimes representing 

 an accumulation of nutrient material which the cells are unable to as- 

 similate, sometimes resulting from the breaking down of the normal 

 combined fats into vacuoles of free fat. It is customary to speak of such 

 cells as "fatty liver cells, ""cartilage cells containing fat, "etc., and to restrict 

 the term "fat cell" to those of mesenchymal origin distended with one or a 

 few large vacuoles. 



Pigment cells are cells of mesenchymal type the protoplasm of which 

 contains colored granules. The granules, which are generally unaffected 

 by stains, appear brown or black in sections, and are composed of melanin 

 in some of its various forms. The changes of color in the chameleon 

 are largely due to the contraction or extension of the processes of such 



