256 HEAT AND PROTOPLASM [Cn. VIII 



(rarely to 125) without all dying. The foregoing cases show 

 clearly that increased resistance capacity is frequently gained 

 by subjecting the protoplasm of the organism to dryness. 



But there are other conditions under which the living sub- 

 stance shows extraordinary resistance capacity. In general, as 

 is well known, the spores of organisms withstand higher tem- 

 peratures than the motile stage, when both are in water. This 

 rule holds for many cases : The spores of some bacteria may be 

 heated for a time above 100 C. without killing them, although 

 their motile stage is killed by 50 to 52 (LEWITH, '90). 

 DALLINGER and DRYSDALE ('74, p. 101) and DALLINGER 

 ('80, pp. 13, 14) have determined maximum temperatures for 

 several Flagellata and their spores in water. While none in 

 the motile stage could withstand a temperature higher than 61, 

 the spores in water withstood maximum temperatures varying 

 between 65.5 and 131 for the different species. 



Have the high resistance capacity of dry protoplasm and that 

 of spores a common cause ? Or, in other words, is the proto- 

 plasm of spores especially free from water ? Many observations 

 make it appear probable that this is so. 



Thus in the case of bacteria, the protoplasm of the spore 

 stage is optically denser and occupies less space than in the 

 motile stage. (Cf. LEWITH, '90.) 



In the case of the ciliate Infusoria, the larger size of the 

 protoplasmic mass makes the comparison of the condition of 

 the protoplasm in the two stages easier. We glean the facts 

 from BUTSCHLI ('89, pp. 1652-1654). As the process of encyst- 

 ment proceeds, the contractile vacuole continues to function, 

 the intervals between its contractions gradually increase, and 

 finally it disappears some time after the encystment is com- 

 pleted. Hand in hand with these changes goes a gradual con- 

 densation of the protoplasm. This condensation BUTSCHLI 

 believes to be due to an excretion of water from the proto- 

 plasm. 



In Actinosphserium the change from the richly vacuolated 

 motile form to the encysted condition is even more marked. 

 As BRAUER ('94, p. 193) has shown, the protoplasmic mass 

 becomes, during the process of encystment, smaller and denser. 

 The loss of water from the protoplasm is without doubt due to 



