EXTRANEOUS SUBSTANCES. 



3T 



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, centre, and focus H. with extreme care. The minute 

 granules within the cells are in active motion, resembling the Brown- 

 ian movement; but with proper conditions the motion may continue 

 for many hours. 



EXTRANEOUS SUBSTANCES. 



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

 come somewhat familiar with the appearance of certain objects which 



FIG. 21. EXTRANEOUS SUBSTANCES. 



A. Cotton fibres, showing the characteristic twist. 



B. Linen fibres, 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. 



are frequently, through accident or carelessness, and often in spite of 

 the utmost care, found mixed with our microscopical specimens. 



