CELL THEORIES. 127 



there need be little doubt that pus-corpuscles are 

 derived from white blood-corpuscles, there also 

 need be no more doubt that they likewise origin- 

 ate both fissiparously and endogenously in the 

 tissues. 



I have used the expression " common or undiffer- 

 entiated corpuscles;" and on this subject it may 

 be necessary to make some remark. The vital 

 powers may be enumerated as irritability or sensi- 

 bility, contractility, nutrition or elaboration of sub- 

 stance, and reproduction. All these properties are 

 possessed by an amceba and by amoeboid cor- 

 puscles. But every separate living organism does 

 not possess them all; there are individuals with- 

 out reproductive power. In like manner, all the 

 vital units do not possess throughout life all vital 

 properties ; but in the process of differentiation 

 one property becomes exalted, while another is lost. 

 Muscular fibres, nerve-corpuscles, the corpuscular 

 elements of peripheral nerve-terminations, and 

 secreting corpuscles illustrate this. All of them 

 have lost the reproductive power ; muscular fibres 

 have exalted contractility, nerve-terminations ex- 

 alted sensibility, and secreting corpuscles a highly 

 developed elaborating power. [In brain-corpuscles 

 the proliferating power may reappear in patho- 

 logical circumstances, but it does so at the expense 



