3 8o 



TRANSMISSION 



point. It seemed at this time that a " stationary point " had 

 been reached, but ultimately Dallinger was able to make slight 

 additions to the temperature, and, "proceeding by slow stages " 

 and for "several years," he succeeded at last in reaching 70, 

 when the experiment was terminated by an accident. 



The exact length of time employed in this experiment is not 

 stated, but it is supposed by Vernon to be approximately six 

 years. Thus these organisms were bred for many generations 

 during the experiment, and it is really a case of race acclimati- 

 zation. The organisms were monads, it is true, which multiply 

 by fission, so that, as Davenport states, " the high temperatures 

 acted upon the same protoplasm at the end of the experiment 

 as at the beginning." Is there any reasonable doubt that this 

 is the process by which organisms of this character have gained 

 access to our hot springs even under natural conditions ? 



In this experiment three points are noteworthy : 



1. There were certain "sticking points," so to speak, that 

 were difficult to get over, but after these were passed, additional 

 increase of heat was easily endured. The temperature of 25.5 

 was one of these sticking points. 



2. It was found that the process of acclimatization did not 

 become gradually slower and more difficult with the higher tem- 

 peratures, for 25.5 was the most difficult temperature encoun- 

 tered, requiring eight months to surmount, while the rise from 

 41.7 to 58.3 was made in seven months, and that from 61.1 

 to 70 in a few months (number not stated), 1 showing that the 

 limits of variability were not reached, and suggesting that the 

 experiment might have been continued much longer and the in- 

 crease pushed much farther. 



3. Organisms acclimated to 70 died off when returned to the 

 original temperature of 15.6, showing that the modification of 

 the protoplasm was not only profound but also permanent. In 

 other words, here is a species whose temperature has been 

 raised through so many degrees, and its protoplasm so altered, 

 that it can no longer endure its original normal temperature. 

 It has been taken entirely out of its field and placed in another 

 so far removed as to have no connection with its former state. 



1 Vernon, Variation in Animals and Plants, p. 380. 



