CIRCri.ATING SYSTEM. 343 



observed between the size of these particles, and that of the 

 body of the animal. The particles of human blood are 

 larger than those of the ox ; while those of the ox are only 

 equal to those of the mouse. Age appears to exercise some 

 influence on their size. Mr HEWSON found in a chicken, 

 on the sixth day of incubation, the particles larger than in 

 a full grown hen ; and also larger in the blood of a very 

 young viper than in that of its mother, out of whose belly 

 it was taken. He could not, however, detect any difference 

 in size between those of a child at its birth, and those of an 

 adult person *. 



Every one is acquainted with the red colour of the blood 

 of the vertebral animals. The colouring matter is not equal- 

 ly diffused, but adheres to the particles, which it surrounds 

 with a thin film. Mr BAUER found an entire particle to be 

 1 7*3 0th part of an inch in diameter, but when deprived of 

 its colouring matter, only 305 o tn P art - While the blood of 

 some animals, as all the vertebrosa, is uniformly of a red co- 

 Jour ; in many other animals it exhibits a different shade. 

 Among the crustaceous animals, as the lobster and shrimp, 

 it is wJtitei while, among some insects, as the grasshopper 

 and white caterpillar, it is green (. 



When blood, newly drawn from an animal, is allowed to 

 rest, it thickens, and spontaneously separates into two parts, 

 a pale coloured fluid termed 'Serum, and a denser coagu- 

 lum, termed Clot, Cnior, or Crassamcntum. The serum 

 is the fluid basis of the blood ; the clot is formed from the 

 floating particles; and hence the difference of colour and 

 consistence exhibited by the two portions. 



During the act of coagulation, a sensible quantity of heal 

 is evolved, amounting to about (Y Fahr. This appears 



Phil. Trans, vol. Ixiii. p. 321. 



t UKWSON, Phil. Trans, vol. Ixiii, p. ,T?t. 



