BLOOD-YESSELS. 133 



can in the same way be made out also to be 

 blood-vessels, containing blood- discs running 

 along at a great pace. Again, down the 

 centre of the transparent body of the fish can 

 be seen, with the unassisted eye, two tiny 

 streaks ; the microscope shows that these 

 also are blood-vessels, and that the blood in 

 the one is running towards the head, in the 

 other towards the tail, A more complete 

 and beautiful demonstration of the circula- 

 tion of the blood never was yet placed under 

 a microscope. The blood in the web foot of 

 a frog is pretty enough ; but it is as a school- 

 boy's daub compared to a painting by Sir 

 Edwin Landseer.* 



* At this point of the lecture the figui-es of four or five 

 young fish were exhibited hy Professor Tyndall, by means of 

 the electric light. The little creatures were magnified to about 

 two feet long, and kicked about famously ou the whitened 



