Sex as an Adaptation 445 
rapidly. They were put back into the beef extract, but it 
failed now to have a beneficial effect, and the animals con- 
tinued to die at a rapid rate. To judge from the appearance 
of the organisms the new decline was due to a different cause; 
for, while in the former periods the food vacuoles contained 
undigested food, at this period the interior was free from food 
masses. The protoplasm became granular and different from 
that of a healthy individual. None of the former remedies 
were now of any avail. ‘When the last of the B-series stock 
had died in the five hundred and seventieth generation (June 
16th), it looked as though the cultures were about to come to 
an end.” Extract of the brain and of the pancreas were then 
tried. To this a favorable response took place at once. The 
organisms became normal in appearance and began to divide. 
After forty-eight hours’ treatment they were returned to 
the usual hay infusion. Here they continued to multiply and 
reached on June 28th the six hundred and sixty-fifth genera- 
tion. 
There can be no doubt that the periods of depression that 
appear in these infusoria kept in cultures can be successfully 
passed if the animals are introduced into a new environment. 
Without a change of this sort they will die. Calkins 
thinks that the effect is produced, not by the new kind of 
food that is supplied, but by the presence of certain chemi- 
cal compounds. The beef extract “does not have a direct 
stimulating effect upon the digestive process and upon divi- 
sion, for, while the organisms are immersed in it, there is a 
very slow division rate; when transferred again to the hay 
infusion, however, they divide more rapidly than before.” 
This brings us back to the idea of the “ renewal of youth” 
through conjugation. Maupas claimed that union of individ- 
uals having the same immediate descent is profitless. Calkins 
suggests that this is due to the similarity in the chemical 
composition of the protoplasm of the two individuals. When 
in nature two individuals that have lived under somewhat 
