THE BLOOD. 219 



In the examination of stains or blood spots, the difficulty is increased 

 by the fact that the drying and subsequent moistening of the globules 

 introduces another element of uncertainty as to their original size. 



Physiological Function of the Red Globules. The red globules of 

 the blood serve mainly as carriers of oxygen. The readiness with 

 which they absorb this substance from the atmosphere, and their changes 

 of color depending upon its supply or withdrawal, indicate that they 

 have a special relation to its introduction and distribution in the body. 

 As a rule, in animals where the red globules are of large size and few 

 in number, the activity of the vital functions is below the average ; while 

 in the species where they are smaller and more numerous, the processes 

 of respiration, circulation, nutrition, and movement are increased in 

 rapidity to a similar degree. The strongly marked physical and chemi- 

 cal characters of the red globules correspond with their importance in 

 the functions of vitality. 



White Globules of the Blood. 



Beside the red globules the blood contains other cellular bodies, differ- 

 ing from the former in several important particulars. These are the 

 white globules. As their name implies, they are destitute of coloring 

 matter, but they present, under the microscope, a glistening appearance, 

 and when collected in large quantity may give to the fluid or clot which 

 contains them a whitish hue. They are much less abundant than the 

 red globules, the average proportion in human blood being one white 

 globule to 300 red. They are nearly spherical in form, and, on the 

 average, 11 mmm. in diameter. They are, accordingly, in human blood, 

 distinctly larger than the red globules. (Fig. 43, c.) They consist of 

 a soft, somewhat viscid, finely granular substance, containing one, two, 

 or three ovoid nuclei. They are less yielding and slippery than the red 

 globules, and adhere more readily to surfaces 'with which they are in 

 contact. When a little watery fluid is added to a drop of blood under 

 examination, the red globules will be hurried away by the currents pro- 

 duced, while the white globules lag behind, and, if the irrigation be con- 

 tinued, may finally be left alone in the field of the microscope. Their 

 transparency is such that, when slowly rolling over with the current, 

 the granules in their interior may often be seen to rotate past each other, 

 with the motion of the globule. The nuclei are sometimes visible in the 

 fresh globule, but may always );< brought into view by the addition of 

 water or of dilute acetic acid. These fluids cause a slight swelling of the 

 globule and an increase of its transparency, by which the nuclei become 

 perceptible as sharply defined ovoid or vesicular bodies, near the central 

 part of the mass. By the prolonged action of acetic acid, a portion of 

 the cell substance becomes condensed about the nuclei in various irregu- 

 lar forms, while the remainder appears transparent and homogeneous, 

 with a delicate circular outline. The final effect of both water and acetic 

 acid is to disintegrate the^ white globules and cause their disappearance. 

 Dilute alkalies dissolve them with great readiness. 



