BLOOD-GLOBULES. 213 



CHAPTER XI. 



THE BLOOD. 



THE blood, as it exists in its natural condition, while circulating 

 in the vessels, is a thick opaque fluid, varying in color in different 

 parts of the body from a brilliant scarlet to a dark purple. It has 

 a slightly alkaline reaction, and a specific gravity of 1055. It 

 is not ; however, an entirely homogeneous fluid, but is found on 

 microscopic examination to consist, first, of a nearly colorless, 

 transparent, alkaline fluid, termed the plasma, containing water, 

 fibrin, albumen, salts, &c., in a state of mutual solution; and, 

 secondly, of a large number of distinct cells, or corpuscles, the 

 blood- globules, swimming freely in the liquid plasma. These glo- 

 bules, which are so small as not to be distinguished by the naked 

 eye, by being mixed thus abundantly with the fluid plasma, give 

 to the entire mass of the blood an opaque appearance and a uniform 

 red color. 



BLOOD-GLOBULES. On microscopic examination it is found that 

 the globules of the blood are of two kinds, viz., red and white ; of 

 these the red are by far the most abundant. 



The red globules of the blood present, under the microscope, a 

 perfectly circular outline and a smooth exterior. (Fig. 54.) Their 

 size varies somewhat, in human blood, even in the same specimen. 

 The greater number of them have a transverse diameter of ^^ of 

 an inch ; but there are many smaller ones to be seen, which are 

 not more than -5^17 or even s^W f an i nca i n diameter. Their 

 form is that of a spheroid, very much flattened on its opposite 

 surfaces, somewhat like a round biscuit, or a thick piece of money 

 with rounded edges. The blood-globule accordingly, when seen 

 flatwise, presents a comparatively broad surface and a circular out- 

 line (); but if it be made to roll over, it will present itself edge- 

 wise during its rotation and assume the flattened form indicated at 

 b. The thickness of the globule, seen in this position, is about 



