324 Problems of Organic Adaptation 



gradually increasing the temperature of the water certain 

 protozoa have been acclimatized to water so hot that other 

 individuals of the same species that have not been so accli- 

 matized are instantly killed and cooked when placed in it. 

 Some animals and plants may undergo complete dessication 

 and yet come out "as good as new" when they are again 

 placed in water. There is a small rotifer that is found in 

 rain gutters and cemetery urns which can be completely dried 

 so that it contains no trace of water. When it is again 

 placed in water, it is not only completely restored, but is 

 found to have renewed its youth. 



Even more remarkable are the adaptations that organisms 

 show to certain poisons, if these poisons are given in graded 

 doses so that the organism acquires a tolerance for them. 

 Such tolerance may be acquired to a limited extent to violent 

 mineral poisons, such as corrosive sublimate, as Davenport 

 showed in the case of Paramecium. It is also known that 

 human beings, as well as other organisms, may acquire 

 tolerance for arsenic and arsenical compounds. One such 

 compound is "salvarsan," and Ehrlich, its inventor, points 

 out the importance of giving it in doses large enough to kill 

 the syphilis organism "mit einem Schlag," since the organ- 

 ism will acquire a tolerance for the poison if it is given in 

 smaller doses. But the poisons to which living things most 

 readily become adapted are those of organic origin, such as 

 alkaloids. It is well known that "drug fiends" may take 

 enough morphine or cocain to kill a man, who is unac- 

 customed to the drug, without any very serious or immedi- 

 ate injury. Similarly, tolerance is gradually acquired for 

 tobacco, alcohol and many other poisons. Among the most 

 striking instances of this is the tolerance to serpent's venom 

 and to bacterial toxins. If the venom of rattlesnakes or 

 cobras is injected into guinea-pigs or rabbits in graded doses, 



