THE TISSUES 25 



or cartilage and ultimately bone, or store up oily mate- Fat cells 

 rial and become fat. Or again, they may develop 



Drawing by R. Weber 



FIG. 5. Development of a fat cell. The black spot is the nucleus. The original 

 cell is of the type of connective tissue cells. Globules of fat are developed in the 

 cytoplasm ; these run together and increase, until at last the whole cell is a mass of 

 fat with a thin outer covering consisting of what is left of the cytoplasm, the nucleus 

 pushed to the wall. In this way material is stored up in the body, to be utilized 

 later as a source of energy. Sometimes cells whose normal function is not that of 

 forming fat behave in a similar manner. The result is fatty degeneration, a very 

 serious disease. Pathological (diseased) states are often due to developments which 

 in another place, or at another time, would be normal and beneficial ; just as crimes 

 are often actions which under other circumstances would be desirable. The per- 

 version of functions is a great source of evil. 



abnormally, and produce tumors (Latin tumor, a swell- 

 ing) dangerous to life. In general terms it may be said 

 that connective tissue cells have special powers of pro- 

 ducing or secreting substances which serve mechanical 

 ends, or, in the case of fat, afford a means of storing 

 up fuel to be later utilized by the body. The material 

 they use is derived from the food, but they have the 

 power of selecting the raw materials and converting 

 them into what may be fairly termed manufactured 

 products. 



4. It is contrary to familiar usage to call the blood a Blood 

 tissue, yet from the standpoint of the physiologist it 

 cannot be otherwise considered. In cartilage we have 

 a number of cells, separated by a solid substance. In 

 blood we similarly have cells, but they are in a fluid 

 medium, the plasma. It is necessarily so, since the 

 blood flows, serving as a means of communication be- 

 tween the various parts of the body. The blood vessels 



