MICROSCOPIC CHROXOPHOTOGRAPHY 299 



which causes an uncertainty of outline, and an inter- 

 ruption of continuity. 



Further, in the reproduction of microscopical photo- 

 graphs, it is always as well to have recourse to thick 

 inks. 



The Movement of the Blood in Capillary Vessels. — 

 The capillaries in the mesentery of a triton serve 

 excellently for this purpose. A layer of the peritoneum 

 is stretched over a piece of cork which has a hole 

 bored through the centre, through which the light 

 can penetrate. A fine capillary is manipulated into 

 the centre of the field on the ground-glass plate. 

 Outside the vessel the extravasated red and white 

 corpuscles are motionless, but within the vessel they 

 are hurried along in a rapid but somewhat inter- 

 mittent stream. If the different members of a series 

 of photographs are compared, it is quite obvious that 

 there is some movement from the changes in arrange- 

 ment which can be noticed among the corpuscles ; the 

 rapidity of movement can be actually estimated by 

 measuring the distance traversed between two successive 

 exposures, namely, the distance traversed in ^jj part 

 of a second. For instance, if the space traversed 

 during five separate exposures is about 4 centimetres, 

 say 20 centimetres per second, and the degree of 

 magnification is about 90 diameters, the actual velocity 

 will be a little more than 2 millimetres per second. 



Hence, what we call the "circulatory torrent," 

 though it appears very swift to the eye, is in reality 

 a very sluggish stream. 



Movement of Zoospores. — In the realm of vegetable 

 Physiology many curious movements are to be noticed ; 

 there is one in particular which we thought would be 

 interesting to reproduce, namely, that of the zoospores 

 within conferva cells. These water-plants are com- 

 posed of filaments consisting of a series of cells 



