CHAPTER X. 

 VITALITY. 



A NOR:\rAL active protozoon is a bit of protoplasm in which the 

 vital activities are perfectly balanced, correlated and coordinated in 

 response to internal and external stimuli. If the physiological bal- 

 ance is disturbed by abnormal activity or inactivity in one or 

 other function the result is evident in the general vitality of the 

 organism. The organization, however, is not rigidly fixed and 

 undergoes adaptive changes in response to the new conditions until 

 activities are again coordinated. The Protozoa thus agree with all 

 protoplasm in having the power of adaptation or ability of the proto- 

 plasmic substances to react to unusual stimuli in such a way as to 

 maintain perfect correlation and coordination under the new con- 

 ditions. 



An interesting case of orderly response to unusual conditions 

 was the fusion of two conjugating individuals of Uroleptis mohilis. 

 Instead of separating at the end of twenty-four to twenty-six hours 

 as in ordinary conjugation, these two individuals remained attached 

 for six days during which time the usual reorganization processes 

 occurred in each. On the seventh day they fused along the entire 

 ventral side, forming a bilaterally symmetrical individual with 

 two oppositely placed mouths and peristomes, two contractile vac- 

 uoles and two independent sets of macro- and micronuclei (Fig. 19-1). 

 On the eighth day this remarkable creature divided three times 

 giving eight double individuals all similar to the original bilaterally 

 symmetrical one from which they came. They continued to divide 

 at the rate of approximately one division per da\' on the average 

 for a period of four hundred and five days and through three hundred 

 and sixty-seven divisions. The interesting fact here is the corre- 

 lation of two distinct sets of structures and functions so as to act 

 harmoniously and synchronously as one individual, and the setting 

 up of an entirely new organization. Had the two indi^'iduals sepa- 

 rated as in normal conjugation their metabolic processes would not 

 have been synchronous, the periods of division would have been 

 more or less similar but not identical. In the double individuals 

 the two sets of eight macronuclei behaved differently in different 

 indi^■iduals. In one case each set would fuse prior to division to 

 form a single ellipsoidal macronucleus (Fig. 195) behaving thus 

 like two normal individuals when ready to divide (p. 222). In the 

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