734 THE PHYSIOLOGY OF THE CONTRACTILE TISSUES 



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 patho- 

 logical products. Engelmann found 

 that the energy of ciliary motion in- 

 creases as the temperature is raised 

 up to about 40 C., after which it 



Fig. 241 Ciliated Cell (M. 

 Heidenhain). From a 

 ' liver duct ' of the garden 

 snail x 2,500. 



Fig. 242. Ciliated Cell (Schneider). 

 From a flatworm (Planocera folium). 

 i, space between two adjoining 

 ciliated cells; 2, basal bodies; 4, 

 inner granule; 5, 'cilia roots'; 

 6, boundary layer. 



diminishes quickly. Over-heating causes cilia to come to rest, but 

 if the temperature has not been too high, and has not acted too 

 long, they recover on cooling, thus exhibiting the phenomena of 

 heat standstill which we have already studied in the heart. 



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 independent motion 

 when severed from the cell-body. It has been observed in certain low 

 forms of animals that cilia which have been broken off from the cell 

 are still able to contract when a small portion of the substance of the 

 cell-body at the point where the cilium is attached to the cell, the 

 so-called basal piece, or basal body (Fig. 242), has come off along with 

 them. In other forms isolated cilia can contract in the absence of 

 anything corresponding to the basal piece. It cannot, therefore, be 

 said that continuity with the basal piece is absolutely necessary. Nor 

 is it known what significance for the ciliary movements is possessed 

 by the long fibrillse, called the ' roots of the cilia,' which in some animals 



