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MANUAL OF PHYSIOLOGY. 



idly past them down the centre of the channel (Fig. 98). This 

 may partly be due to their peculiar adhesiveness, which also causes 

 them to stick to the glass slide, whilst the red disks are washed 

 away when a little stream of saline solution is allowed to flow 

 under the cover-glass. These cells show all the manifestations of 

 activity characteristic of independent living beings. If kept in 

 a medium suitable to them, and at the temperature of the body, 

 they will be seen soon to alter their appearance ; their outline 

 becomes faint, they are no longer spherical, but very irregular in 



FIG. 98. 



Vessels of the Frog's Web. (a) Trunk of vein, and (6 6) its tributaries 

 passing across the capillary network. The dark spots are pigment cells. 



shape, and constantly change their form by sending out and re- 

 tracting delicate processes, by means of which they change their 

 position, so that they may be said to perform locomotion. These 

 movements are rendered more active by a slight increase of tem- 

 perature, and are checked by cold. For continued observation, 

 about 38 C. is the best temperature. They respond to many 

 other influences, such as electricity, etc., even for a considerable 

 time after removal from the body. 



