THE CKLL DOCTRINE. 105 



though partial ctirrents also exist which take differ- 

 ent routes ; so that sometimes trains of granules 

 may be seen coursing swiftly in opposite directions, 

 within a twenty-thousandth of an inch of each other; 

 and occasionally opposite streams come in direct col- 

 lision, and after a longer or shorter struggle one pre- 

 dominates. The cause of these currents seems to lie 

 in contractions of the protoplasm which bounds the 

 channels in which they flow, but which are so minute 

 that the best microscopes show only their effects and 

 not themselves. 



Among the lower plants it is the rule rather than 

 the exception, that contractility should be still more 

 openly manifested at some periods of their existence. 

 The protoplasm of Algas and Fungi becomes,'' under 

 many circumstances, partially or completely freed 

 from its woody case, and exhibits movements of its 

 whole mass, or is propelled by the contractility of 

 one or more vibratile cilia. 



In illustration of animal protoplasm. Prof. Huxley 

 adduces the colorless corpuscles of the blood, which, 

 under the microscope, at the temperature of the body, 

 exhibit a marvellous activit}"^, changing their forms 

 with great rapidity, drawing in and thrusting out 

 prolongations of their substance, and creeping about 

 as if they were independent organisms. " The sub- 

 stance which is thus active is a mass of protoplasm, 

 and its activity differs in detail rather than in prin- 

 ciple from that of the protoplasm of the nettle. Under 

 sundry circumstances the corpuscle dies, and becomes 

 distended into a round mass, in the midst of which 

 is seen a smaller spherical body, which existed, but 



