Page:Popular Science Monthly Volume 19.djvu/479

Rh 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, something like a sponge? It is believed that the red corpuscles are produced from the white, being only their modified nuclei. They are more numerous in the capillaries and veins. The death and reproduction

 A, red corpuscles, lying in rows like rolls of coin; at a and a are seen two white corpuscles. B, red corpuscles more highly magnified, seen in face; 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 puckered or crenate all over; I, the same, at the edge only.

of the blood-corpuscles are rapid and constant. Dr. Draper estimates 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, entangling the corpuscles, forms the clot leaving a yellowish liquid called serum. The composition of the blood may be graphically shown as follows:

Coagulation serves in nature the purpose of stopping wounds. It is providentially more rapid in the lower animals, as they have no artificial 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