THE BIOLOGY OF THE CELL SURFACE 



extremely tenuous as they move along a delicate track, such 

 as the thread of a spider's web, which behavior I interpret 

 as a pseudopod extending in one direction. 



Concerning the cause of migration, two views are main- 

 tained. According to one, the cells react positively to 

 solids; according to the other, the cells move away from 

 regions of too high acidity. My own interpretation is that 

 cells in tissue-culture are no longer under the restraint 

 imposed upon them when they stand in coordination with 

 and subordination to their normal environment, i.e., other 

 cells and tissue fluids. Thus their ectoplasmic activity is no 

 longer ordered and controlled by the contact but is exagger- 

 ated especially in their free and exposed surfaces — that is, 

 in the regions where they are not in contact with the cells 

 of the bit of tissue implanted on the medium. Hence, they 

 migrate away from the mass. 



Suspended in the blood-plasma of vertebrates are red 

 blood corpuscles. In mammals these are devoid of nuclei 

 and therefore not true cells. All other vertebrates possess 

 nucleated red blood cells. The structure of these latter has 

 been worked out by Meves, who found that they have a 

 well-marked ectoplasm. 



The blood of vertebrates contains in addition to the red 

 blood corpuscles the leucocytes or white blood cells. In 

 human blood these cells are sub-divided into four kinds, 

 cell-size, staining reaction of cytoplasmic granules, and 

 nuclear form being the characters on which the sub-divisions 

 are made. In a healthy adult individual there is a fairly 

 constant number of each type of white blood-cell. This 

 number is used as an index for pathological states — many 

 diseases have each a characteristic "blood-picture" which 

 is an important diagnostic aid. On these highly interesting 

 cells ectoplasm can be easily demonstrated. It has largely 

 been assumed that for phagocytic activity and movement of 

 white blood cells the same theories hold that have been 



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