THE BLOOD AND ITS CIRCULATION 



463 



to this, " contractile vacuoles have been observed in the colorless blood- 

 corpuscles of amphibia under certain conditions." Is it possible that 

 the human body is an aggregation or colony of low individuals, some- 

 thing like a sponge ? It is believed that the red corpuscles are pro- 

 duced from the white, being only their modified nuclei. They are 

 more numerous in the capillaries and veins. The death and reproduc- 



FiG. 4. Red and White Corpuscles of Human Blood greatly magntfted. A, red corpus- 

 cles, lying in rows like rolls of coin ; at a and a are seen two white corpuscles. B, red cor- 

 puscles more highly magnified, seen in lace ; C, the same in profile ; D, the same in rows more 

 highly magnified ; E, a red corpuscle swollen into a sphere by absorption of water. F, a white 

 corpuscle magnified same as B. G, the same, throwing out some blunt processes ; K, the same, 

 treated with acetic acid, showing nucleus, magnified the same as D. H, red corpuscles puck- 

 ered or crenate all over ; I, the same, at the edge only. 



tion of the blood-corpuscles are rapid and constant. Dr. Draper esti- 

 mates that twenty millions die at every breath. In transfusion of the 

 blood of a bird into a mammal, the bird-corpuscles soon disappear. 



Upon exposure to the air the fibrine of the blood hardens, and, en- 

 tangling the corpuscles, forms the clot^ leaving a yellowish liquid called 

 serum. The composition of the blood may be grajDhically shown as 

 follows : 



' Corpuscles \ C*-d ^ ^ ^^^^ 



i Fibrine 



Liquid blood 



1 



Plasma, or s 



Liquor sanguinis ( 



Serum 



\ Albumen 



{ Serosity = water and salts ^ 



[ Coagulated 

 ^ blood. 



Coagulation serves in nature the purpose of stopping wounds. It 

 is providentially more rapid in the lower animals, as they have no arti- 

 ficial means of arresting the flow of flood ; and quite instantaneous in 

 insects. What prevents the blood from coagulating during life, or in 

 the blood-tubes, is unsettled. It can be prevented by salt. 



The temperature of the blood depends upon the rapidity with 



