220 



FUNCTIONS OF NUTRITION. 



FIG. 48. 



Amoeboid Movement of the White Globules. This movement is so 

 called from its resemblance to those of Amosba, a minute animal form, 



of simple organization, living in 

 fresh -water pools and ditches. 

 It is never perceptible while the 

 blood is circulating normally 

 in the blood-vessels, where the 

 white globules always present 

 a rounded and uniformly granu- 

 lar appearance But soon after 

 the blood has been withdrawn, 

 if maintained at or near its nor- 

 mal temperature, the white glob- 

 ules may be seen to alter their 

 shape in a remarkable way A 

 portion of the rounded outline 

 of the globule first becomes faint 



and irregular, flattening out and 



WHITE GLOBULES OF HUMAN BLOOD ; altered by extending itself into One or more 

 dilute acetic acid. 



transparent, homogeneous-look- 

 ing prolongations. These prolongations are alternately protruded and 

 retracted, sometimes extending into long filamentous processes, some- 

 times into shorter expansions with rounded ends. The variations in 

 form thus produced succeed each other with different degrees of rapidity, 

 according to circumstances. In man and the warm-blooded animals, 

 the blood requires to be kept at about the temperature of the living 

 body, in order that these appearances may be exhibited; but in the 

 cold-blooded animals they may be shown at the ordinary temperature 

 of the air. 



Beside these changes of form, the white globules of the blood may 

 sometimes be seen, by a similar mechanism, to move from place to 

 place. In these cases, the globule first sends out the pale prolonga- 

 tions above described. The granules of the remaining portion are then 



FIG. 49. 



CHANGES IN FORM OF A WHITE BLOOD-GLOBULE of the Newt (Triton niiUepunctalus), occurring in 

 an interval of seven minutes, and within half an hour after its extraction from the living body. 



propelled, by a kind of flowing movement, into the prolongations, 

 which thus become granular, and at the same time assume a more 

 rounded form. The remaining portion is subsequently drawn after 



