BLOOD. 



31 



Taking this drop of blood from my Ungcr as a 

 standard of comparison, "we find, on applying tlie mi- 

 crometer, that the disks run from l-2500tli to l-5000tli 

 of an inch ; but that the great majority are about 

 l-3300tli in diameter. On these slides are samples of 

 other kinds. This is the blood of a Fish, — the common 

 Blenny or Shanny {Blennius 2)^^olis). Here Ave see 

 at once the oval form of the disks ; their average is 

 l-2800th by l-3300th of an inch. Here is the blood of a 

 Frog {Rana temporaria) ; these are more than twice 

 the size of the fish's ; for thev averac-e l-1250th bv 

 l-1800tli of an inch. And, finally, I can show you a 

 drop of blood from this Smooth-newt {Lissotriton punc- 

 tatus). Tlie large size of the disks is now conspicuous, 

 and so indeed is the elegance of their form : in this 

 case, as in the last, we see in each disk a distinct round- 

 ish nucleus. These run from 1-TOOth to l-950th in 

 length, by 1-llOOth to 1-lGOOth in breadth ; but the 

 average are about 1-SOOth by l-1300th of an inch. 



a Man. 



BLOOD-DISKS. 



i Bleiiiiy. c Frog. d Newt. 



It may interest you to see these blood-disks in their 

 jiroper situation, and to observe the motion wliieh 



