HAND-BOOK OF PHYSIOLOGY. 



through the walls of the blood-vessels (p. 159), by Waller, whose obser- 

 vations were confirmed and extended to connective tissue corpuscles by 

 the researches of Recklirighausen, Cohnheim, and others, and thus the 

 phenomenon of migration has been proved to play an important part in 

 many normal, and pathological processes, especially in that of inflam- 

 mation. 



This amoeboid movement enables many of the lower animals to capture 

 their prey, which they accomplish by simply flowing round and enclosing it. 



The remarkable motions of pigment-granules observed in the branched 

 pigment-cells of the frog's skin by Lister are probably due to amoeboid 

 movement. These granules are seen at one time distributed uniformly 

 through the body and branched processes of the cell, while under the 

 action of various stimuli (e.g., light and electricity) they collect in the 

 central mass, leaving the branches quite colorless. 



(b.) Ciliary action must be regarded as only a special variety of the 

 general motion with which all protoplasm is endowed. 



The grounds for this view are the following: In the case of the Infu- 

 soria, which move by the vibration of cilia (microscopic hair-like processes 

 projecting from the surface of their bodies) it has been proved that these 

 are simply processes of their protoplasm protruding through pores of the 



FIG. 2. Human colorless blood-corpuscle, showing its successive changes of outline within ten 

 minutes when kept moist on a warm stage. (Schofield.) 



investing membrane, like the oars of a galley, or the head and legs of a 

 tortoise from its shell: certain reagents cause them to be partially re- 

 tracted. Moreover, in some cases cilia have been observed to develop from, 

 and in others to be transformed into, amoeboid processes. 



The movements of protoplasm can be very largely modified or even 

 suspended by external conditions, of which the following are the most 

 important. 



1. Changes of temperature. Moderate heat acts as a stimulant this 

 is readily observed in the activity of the movements of a human colorless 

 blood-corpuscle when placed under conditions in which its normal tem- 

 perature and moisture are preserved. Extremes of heat and cold stop the 

 motions entirely. 



2. Mechanical stimuli. When gently squeezed between a cover and 

 object glass under proper conditions, a colorless blood-corpuscle is stimu- 

 lated to active amoeboid movement. 



3. Nerve influence. By stimulation of the nerves of the frog's cornea, 

 contraction of certain of its branched cells has been produced. 



4. Chemical stimuli. Water generally stops amoeboid movement, and 

 by imbibition causes great swelling and finally bursting of the cells. 



