CLASSIFICATION OF TISSUES 



53 



radiating filaments at the poles of the cells present figures which 

 have been compared by Wilson to the arrangement of iron filings 

 about the poles of a horseshoe magnet. The circle of radiating 

 filaments at each pole is called the attraction- sphere, the center of 

 which is the centrosome. It is possible that the substance of the 

 filaments serves to draw the chromosomes apart. Apparently the 

 centrosome is to be regarded as a permanent organ of the cell. 

 Its division must precede the division of the nucleus. 



The time required for cell division in man is about half an 

 hour (Stohr). 



Most of the stages in karyokinesis may be demonstrated in the epithelial 

 cells in the tail of a young newt or salamander tadpole. Fix in Flemming's 

 osmie acid or chromic -acetic solution for twenty-four hours; wash; stain with 

 safranin or hsematoxylin ; and, after dehydrating and clearing, mount in balsam. 

 Examine with oil -immersion lens, if possible. 



CLASSIFICATION OF TISSUES 



Histology, or microscopical anatomy, treats of the minute 

 structure of the tissues and organs of the body. 



A tissue is a collection of similar cells and intercellular sub- 

 stances. The principal tissues are epithelial, connective, muscular, 

 and nervous. Blood is sometimes considered as a tissue. Most 

 organs are made of several different tissues. /The following table 

 shows the varieties of tissues: / 



Epiilielial Tissue { 

 < 



Connective Tissue 



Columnar. 

 Endothelium. 

 Blood. 



Mucoid. 



White Fibrous. 



Yellow Elastic. 



Adipose. 



Retiform (of lymphoid tissue), 



Cartilaginous. 



Osseous. 

 L Dentine. 



{Unstriated. 

 Striated. 

 Cardiac. 

 Nervous Tissue. 



