UFFENBACH’S INTERVIEW 65 
through the venae, which have no valvulae. Besides, it 
is surely impossible to distinguish whether the pulse at 
the wrist beats downwards or upwards? But this by 
the way.—Mr. Leeuwenhoek then cut off with a knife a 
small bit from a mussel,’ such as they are here wont to 
eat, and showed us that all its parts were in a continuous 
motion ; just as a snake apparently continues to move 
itself for a long time when freshly hacked to pieces with 
a switch. In both cases this is due to the vital spirits, 
which seek to escape, and so bring about the movements. 
Afterwards Mr. Leeuwenhoek cut a mussel in two through 
the middle, in order to show us how the eggs and young 
mussels are generated. He also showed us certain black 
dots, which he maintained were young mussels in their 
black shells; but we couldn't take them for such, being 
unable to distinguish them. He also cut the gut of a 
mussel in two, and showed us, by means of his micro- 
scopium, a great mass of sand in it, which the mussels 
presumably take in with the slime in which they live. 
Mr. Leeuwenhoek considered, and not unjustly, that this 
sand serves for the formation of the shells of their young 
ones, just as hens and other birds readily eat sand and 
lime for the sake of their egg-shells. He wished also to 
show us the circulation of the blood in an eel, only the 
creature was too big and black. Mr. Leeuwenhoek makes 
this experiment with an instrument which . . . is 
simple, large, and not at all convenient. The one made 
by Mez in Amsterdam, with a camera obscura, is better ; 
with this one you are dazzled by the light and the glass. 
Mr. Leeuwenhoek showed us the circulation of 
fee blood very well with this machine, though it was 
somewhat troublesome to manipulate, and would be even 
worse for making observations lasting over a long time, 
because you have to put the side of the mcroscopwwm, 
where the lens is, against your forehead, and look 
1 No doubt L. showed the ciliary motion on a portion of the gill of 
Mytilus—as he well knew how. 
5 
