60 AGE, GROWTH, AND DEATH 



lengthwise and you see not only that each hair con- 

 sists of various parts, but also that the cells in these 

 parts are unlike. The follicles within the skin in 

 which the hair is lodged likewise have walls with cells 

 of various sorts. It may interest you also to point 

 out in the figure the little muscle, Ap, which runs 

 from each hair to the overlying skin, so disposed that 

 when the muscle contracts the "particular hair will 

 stand up on end." Still more clearly does the variety 

 of cells which actually exists in a hair show in the 

 following picture (Fig. 18), which represents a cross- 

 section of a hair, and its follicle, but more highly 

 magnified than were the hairs in the previous figure. 

 The adult body consists of numerous organs. 

 These are joined together and kept in place by inter- 

 vening substance. The organs themselves consist 

 of many separate parts which are also joined by a 

 substance which keeps them in place. This sub- 

 stance has received the appropriate name of connec- 

 tive tissue. We find in the adult that it consists of a 

 considerable number of structures. There are cells 

 and fibres of more than one kind, which have been 

 produced by the cells themselves. There is more or 

 less substance secreted by the cell which helps to give 

 consistency to the tissue. In some cases this sub- 

 stance, which is secreted by the cells, becomes tougher 

 and acquires a new chemical character. Such is 

 the case, for instance, with cartilage. Or, again, you 

 may see a still greater chemical metamorphosis going 

 on in the material secreted by the cells in the case 



