244 



Merkel Henry 'Jacobs 

 c Effect of Duration of Desiccation 



The effects so far considered have been those due to the condi- 

 tions under which drying occurred. It has been seen that the 

 rapidity of the drying has a very important relation to the ultimate 

 effect of the process and that the temperature at which it occurs 

 is also of importance. There are other effects, however, which do 

 not depend on the conditions under which the desiccation occurs, 

 for example, it has long been known that the duration of the desic- 

 cation must be taken into account. Other things being equal, 

 the longer the rotifers are kept the smaller are their chances of 

 recovery. This fact has been noticed by numerous observers; 

 Davis was unable to revive rotifers that had been kept dry under 

 natural conditions for a year. The following table, based on experi- 

 ments made on rotifers dried fairly rapi3ly in the absence of sand 

 illustrates the relation that exists between the duration of the desic- 

 cation and the mortality. The rotifers all came from the same 

 culture and were dried under exactly the same conditions at the 

 same time. 



TABLE VII 



Effect of duration of Desiccation 



d Effect of Alternations of Moisture and Dryness 



Since the conditions of drying in the preceding experiments 

 were the same in each case the difference in mortality observed 

 must be due to some progressive change or changes that continue 

 throughout the entire period of desiccation, the only variable fac- 

 tor being that of time. The question arises as to the cause of the 



