2. But if he did keep them free from such products, by changing the fluid every day or oftener, no degeneration took place. He thus kept Glaucoma for 683 generations, without a sign of degeneration, and similar results were reached with other species.
Enriques concluded that the results of Maupas and Calkins are explained by these observations. In their experiments, he holds that the continued action of bacterial products was the cause of the degeneration.
Every one with experience in such work must I believe agree with Enriques that bacterial action is a most important factor in producing degeneration and death. But it seems clear that he was in error in holding that this is the only cause. The most significant feature of his results was the fact that he kept his organisms more than twice as long as did Maupas, with no degeneration whatever. He kept them for very nearly the same number of generations as did Calkins, but in the latter's cultures there had been several crises of degeneration, which finally ended in destruction. Enriques's work indicated strongly that this degeneration was not inevitable, though he may not have explained with full adequacy why it occurs. Enriques drew the general conclusion that there is no such thing as senile degeneration in these organisms; they might enjoy perpetual youth and live without end, if only the conditions are kept healthful.
Then came the work of Woodruff, with which you are acquainted; work which appears to be definitive for the part of the problem with which it deals. Woodruff investigated the possibility that the degeneration observed by Maupas and Calkins may have been due to too great uniformity in the cultural conditions; or to the fact that the conditions employed lacked something necessary to the continued health of the animals.
He therefore carried on a set of experiments wherein certain lines were subjected to frequent changes in conditions, while others were kept uniform. As you know, this gave the key to the problem. At last accounts, the progeny of a single individual were flourishing in generations subsequent to the 2,500th, after four years and three months, without conjugation. They had been at that time kept for about four times as many generations as had Calkins's culture when it died out, yet the animals in Woodruff's experiment showed no indication of degeneration. Later work by Woodruff seems to show that if only the culture medium is properly selected, no degeneration occurs even if the conditions are kept uniform.
The work of Woodruff demonstrates that the very limited periods within which Maupas and Calkins observed degeneration has no significance for the question as to whether degeneration is an inevitable result of continued reproduction without conjugation. In other words, it annihilates all the positive evidence for such degeneration, drawn