THE BLOOD. 



255 



weeks of the fasting period. In the new-born the number is greater 

 than in adults 17,000 to 20,000 per cubic millimeter. Cabot states) 

 that 30,000 is never a high count after a meal in infants under two 

 years. In the later months of 

 pregnancy, especially in primi- 

 parae, the number increases to 

 16,000 to 18,000. Many patho- 

 logic conditions of the body also 

 influence the count very con- 

 siderably. 



The method for counting the 

 white corpuscles is similar to that 

 used in counting the red. The 

 given volume of blood should, 

 however, be diluted with 10 vol- 

 umes of a olie-tmrd of one per 



cent. solution""" of acetic"""a'c1d, 

 which renders' the red corpuscles 

 invisible and thus facilitates the 



FIG. 109. HUMAN LEUKOCYTES SHOW- 

 ING AMEBOID MOVEMENTS. 



counting of the white. The pip- 

 ette should have a "larger bore 

 than that used for the red, and a greater number of squares in the 

 counting chamber should be counted, so as to diminish the percent- 

 age of error. 



Physiologic Properties. The white corpuscles possess the 



characteristic property of 

 exhibiting movements simi- 

 lar to those observed in the 

 amoeba, and are therefore 

 termed ameboid. These 

 movements consist in alter- 

 nate protrusions and re- 

 tractions of portions of the 

 cell body, as a result of 

 which they exhibit a great 

 variety of forms. (See Fig. 

 109.) The protruded pro- 



FIG. HO.-SMALL VESSEL OF A FROG'S MESEN- CeSS Can al ? a " ach itself 

 TERY SHOWING DiAFEDEsis. iv, w. Vas- to some point oi me sur- 



cular walls, a, a. Poiseuille's space, r, f ace on which it rests, arid 



pushes the i,, C ant:: Hn then draw the body of the 



various stages of extrusion. /, /. Ex- corpuscle after it. By a 

 truded corpuscles. (Landois and Stirling.} repetition of this process 



the corpuscle can slowly 

 creep about and change its position in space. In virtue of these 



