LECTURE Xll. 
221 
pearance which it exhibits is such as to alarm the 
superstitious with the idea of the water being 
changed into blood; a panic of which numerous 
instances have been adduced by authors, and 
•which is the more excuseable in those who are 
ignorant of the cause, as the animalcules are so 
very small as to be utterly imperceptible, except 
to an uncommonly acute eye, without the assist- 
ance of the Microscope; so that even taking up 
and examining it affords no satisfactory eluci- 
dation to the vulgar. I remember to have more 
than once seen the whole surface of a large pond 
thus covered with this animalcule, of which there 
was not the least appearance the preceding day. 
It should be observed that some other animals, 
and particularly some small insects of the genus 
Monoculus, have occasionally produced a similar 
appearance : but in that case the demonstra- 
tion becomes easy; since every one, on taking 
up the water, perceives the red insects. We are 
assured by Swammerdam that the whole city of 
Leyden was one morning in a state of consterna- 
tion on discovering that the waters of that place 
were apparently changed into blood; but the phi- 
losopher soon had the satisfaction of undeceiving 
