DESICCATION IN PHILODINA ROSEOLA. 385 



The Mechanism of Metabolism in the Dried Rotifer. 



Admitting that the desiccation of Philodina is complete and 

 admitting further that metabolism takes place though much 

 retarded, in the dried condition, the mechanics of the metabolic 

 activity is the next point to demand explanation. 



It will be remembered that Jacobs ('09) showed by means of 

 intra vitam staining with chemical indicators and subsequent 

 tests with various gases, that the integument of the dried rotifer 

 is at all times freely permeable to gases. Attention was called, 

 in another paragraph of this paper, to the fact that many animals 

 when deprived of their normal supply of moisture could still 

 exist for a time by means of the direct action of oxygen from 

 the air upon the complex materials of the tissues or upon in- 

 clusions of complex food materials within the latter. This 

 action would of course not be sufficient to prolong life indefinitely 

 for the time would come when all the available reserve food 

 material would be exhausted or the accumulation of poisonous 

 waste products might end life. That such a state of affairs 

 might be realized in the case of a dried Philodina in the air is 

 not impossible. Certain it is that this animal can live a long 

 time; many years in fact, in a dried condition without food from 

 external sources. Its lease of life, however, under these con- 

 ditions, is not indefinite as is evidenced by the fact that under 

 the most careful conditions of drying some of the rotifers always 

 die. To explain these fatal cases it would seem that the store of 

 reserve material became exhausted or the metabolic products 

 accumulated in too great a quantity and death was the result. 

 It seems reasonable to assume then, that under the conditions 

 just outlined metabolic activity goes on through oxidations of 

 complex substances within the tissues of the animal by means 

 of oxygen obtained by direct respiration. 



Those rotifers which were described as having been kept in 

 an evacuated desiccator for varying periods and which survived 

 the experiment could not have their metabolic activities ex- 

 plained upon the same basis as the ones which were dried in air. 

 It will be recalled that mention was made of certain cases where 

 metabolism might proceed in the absence of air by means of 

 intra-molecular activity. In these cases the complex substances 



