100 THE SMALLEST LIVING THINGS 



hours there will be eight individuals of Didinium and not one 

 Paramecium ! 



It occasionally happens, especially with forms that have been 

 maintained for long periods on the same diet, that the proto- 

 plasm becomes loaded with unassimilated food reserves or with 

 the waste products of metabolism. Figure 57 illustrates a Para- 

 mecium in such a condition; in this case it was restored to normal 

 condition by a brief treatment with potassium phosphate and 

 with the salts contained in a dilute solution of beef extract. 



Defecation 



Defecation is the function of eliminating from the body sub- 

 stances which cannot be digested. In the rhizopod types there is 

 no definite spot where such elimination occurs, but in the more 

 complex infusoria a definite anal opening is present (Fig. 3, 

 page 10) . 



