THE BLOOD 



257 



cubic millimeter, after which it rose to 1530, where it practically remained 

 for the succeeding three weeks of the fasting period. 



When the number of leukocytes present in the peripheral blood exceeds 

 the normal, i.e., 10,000 per cubic millimeter the condition is termed leuko- 

 cytosis; when the number falls below the normal the condition is termed 

 leukopenia. Both conditions, however, may be only temporary and therefore 

 physiologic, or they may be permanent, associated with certain diseased states 

 of the body and therefore pathologic. It is therefore permissible to speak 

 of a physiologic and a pathologic leukocytosis and 

 leukopenia. 



The method for counting the white corpuscles 

 is similar to that used in counting the red corpus- 

 cles. The given volume of blood should, however, 

 be diluted with 10 or 20 volumes of a one per cent, 

 solution of acetic acid, which disintegrates the red 

 corpuscles and thus facilitates the counting of the 

 white. The pipette should have a larger bore than 

 that used for the red, and a much greater number 

 of squares in the counting chamber should be 

 counted, so as to diminish the percentage of error. 



Physiologic Properties. The white corpuscles 

 and especially the leukocytes possess the character- 

 istic property of exhibiting movements similar to 

 those exhibited by the amoeba, and are therefore 

 termed amoeboid. These movements consist in al- 

 ternate protrusions and retractions of portions of the 

 cell body, as a result of which they present from mo- 

 ment to moment, a great variety of forms. (See 

 Fig. 108.) The protruded process, the pseudopod, 

 can also attach itself to some point of the surface 

 on which it rests, and then draw the body of the 

 corpuscle after it. By a repetition of this process 

 the corpuscle can slowly creep about and change 

 its position in reference to its environment. By 

 virtue of these amoeboid movements the corpuscle 

 can appropriate small particles of pigment, such 

 as indigo or carmine, and after a short time elimi- 

 nate them from various parts of the surface. It 

 is also capable of thrusting a process into and through the wall Jof the 

 capillary vessel, after which the remainder of the corpuscle follows (Fig. 

 109). This continues until the corpuscle is outside the vessel and in the 

 lymph-space, where it resumes its original shape and movement. This 

 process is best observed in inflammatory conditions, when the blood has 

 come to rest and the vessels are occluded with both red and white corpuscles. 

 To this passage of the white blood-corpuscles through the capillary wall 

 the term diapedesis is given. The movements of the white corpuscles are 

 increased by a rise in temperature up to 4OC., beyond which they cease, 

 owing to the coagulation of the cell-substance. A low temperature also 

 arrests the movements. Induced electric currents also cause contraction 

 and death of the cell. Moisture and oxygen are necessary to their activity. 

 17 



FIG. 109. SMALL VES- 

 SEL SHOWING VARIOUS 

 STAGES IN THE DIAPEDESIS 

 OF LEUKOCYTES. (G. Bach- 

 man.) 



