LECTURE XII. 221 



pearance which it exhibits is such as to alarm the 

 superstitious with the idea of the water being 

 changed into blood 3 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 s_o 

 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 



