EXTRANEOUS SUBSTANCES 



47 





ceases after a short time. The movement has been attributed to 

 several causes. 



Vital Movements. Place a drop of decomposing urine on a 

 slide, cover, and focus with H. The field contains innumerable 

 minute spherules and rods (bacteria) which are in active motion, 

 resembling somewhat the Brownian movement, although sufficiently 

 distinctive after close observation. 



After having rubbed the tongue for a moment against the inner 

 surface of the cheek, put a drop of saliva on a slide, cover, and 

 focus (H) . Among the numerous thin, nucleated scales and debris, 

 small granular spherules the salivary corpuscles will be found. 

 Select one of the last, center, and focus (H) with extreme care. The 

 minute granules within the cells are in active motion, resembling 

 the Brownian movement, but with proper conditions the motion 

 may continue for many hours. 



EXTRANEOUS SUBSTANCES 



Before we begin the study of animal tissues, we wish to have you 

 become somewhat familiar with the appearance of certain objects 



FIG. 24. EXTRANEOUS SUBSTANCES. 



A. Cotton fibers, showing the characteristic twist. 



B. Linen fibers, with transverse markings, indicating segments. 



C. Wool. The irregular markings are produced by the overlapping of flattened cells. Wool 

 may be distinguished from other hairs by the swellings which appear at irregular intervals in the 

 course of the former. 



D. Silk. Smooth and cylindrical. 



