134 THE TISSUES. 



which they are washed in 90% alcohol, dehydrated, cleared in xylol, 

 and mounted. The boundary-sheaths are stained bluish-black, the bone 

 cells dark blue, and the bone substance light blue. 



Fibers of Sharpey. Sections treated by Ranvier's method show the 

 perforating fibers of Sharpey as bright, sharply defined ribbons, appearing 

 as streaks or circles, according to the section made (longitudinal or trans- 

 verse). If decalcified specimens be first rendered transparent by glacial 

 acetic acid, and then immersed for a minute in a concentrated aqueous 

 solution of indigocarmin, washed with water, and then mounted in gly- 

 cerin or Canada balsam, the fibers of Sharpey will appear red and the 

 remaining structures blue. Thin sections of bone can be deprived of 

 their organic elements by bringing them for from one-half a minute to a 

 minute into a platinum crucible at a red heat. In such preparations cal- 

 cified Sharpey's fibers may be seen (Kolliker, 86). 



Virchow's bone corpuscles may be isolated in the following 

 manner : Very thin fragments or discs of bone are immersed for some 

 hours in concentrated nitric acid. They are then placed on a slide and 

 covered with a cover-glass ; pressure with a needle upon the latter will 

 isolate the lacunae, and occasionally also their numerous processes, the 

 canaliculi. 



C MUSCULAR TISSUE. 



Almost all the muscles of vertebrates have their origin from the 

 middle germinal layer. In the simplest type the protoplasm of the 

 formative cell changes into contractile muscle substance, the cell in 

 the meantime undergoing a change in shape (unstriped muscle-cell). 

 In other cases contractile fibrils are formed which are separated by 

 the remains of the undifferentiated protoplasm (striped muscle-cells). 

 In this case the cells either increase very little in length and possess 

 only a single nucleus (heart muscle), or they grow considerably 

 longer and develop many nuclei (voluntary skeletal and skin 

 muscles). 



A peculiarity of muscle-substance is that it contracts in only 

 one direction, while undifferentiated protoplasm contracts in all 

 directions. 



J. NONSTRIATED MUSCLE-CELLS. 



The smooth, unstriped, or nonstriated muscle-cells belong to 

 involuntary muscle, and are found in the walls of the intestine, 

 trachea, and bronchi, genito- urinary apparatus, blood-vessels, in 

 certain glands, and also in connection with the hair follicles of the 

 skin. The involuntary muscle-cells are spindle-shaped cells, which 

 are 40-200 // long and 3-8 // broad. The longest are found in the 

 pregnant uterus, where they attain a length of 500 p. At the thick- 

 ened middle portion of the cell is a long rod-like nucleus, typic of 

 this class of cells. Nonstriated muscle-cells are doubly refractive 

 anisotropic. The cell substance is longitudinally striated, the 

 striation being due to relatively coarse fibrils situated in the outer 



