MUSCLE 



629 



and allowing the cilia, like an immense number of feet, to carry 

 it up an inclined plane. Bowditch found in this way that the 

 cilia on a square centimetre of mucous membrane did nearly 

 7 gramme-millimetres of work per minute (equal to the raising 

 of 7 grammes to a height of a millimetre) . 



Since the cilia in the respiratory tract all lash upwards, they 



must play an important part in 

 carrying up foreign particles taken 

 in with the air, and the mucus 

 in which they are entangled, as 

 well as pathological products. En- 

 gelmann found that the energy of 

 ciliary motion increases as the tem- 

 perature is raised up to about 40 C., 

 after which it diminishes quickly. 

 Over-heating causes cilia to come 

 to rest, but if the temperature has 



FIG. 217. CILIATED CELL 

 (M. HEIDENHAIN). 



From a ' liver duct ' of 

 the garden snail x 2,500. 



FIG. 218. CILIATED CELL 

 (SCHNEIDER). 



From a flatworm (Planocera 

 folium), i, space between two ad- 

 joining ciliated cells ; 2, basal bodies ; 

 4, inner granule ; 5, ' cilia roots ' ; 

 6, boundary layer. 



not been too high, and has not acted too long, they recover on 

 cooling. 



It is not well understood in what way the contraction of the 

 cilia depends upon their connection with the body of the ciliated 

 cell. Very few cases occur in which cilia have the power of inde- 

 pendent motion when severed from the cell-body. It has been 



