71 



are killed when frozen at a few degrees below zero ; some, 

 however, resist - 30° or - 40° ; some others are killed by 

 cold at temperatures above zero. 



VI. METAZOA 



In the sections of this chapter in which the investiga- 

 tions are more closely coordinated toward the solution of 

 some fundamental problems, we shall follow the chrono- 

 logical order so as to show in a clearer manner the his- 

 torical development of these problems. 



1. Coelenterates. Payne (1930) investigated the action 

 of repeated freezings on the coelenterates, Mnemiopsis 

 leidyi and Pennaria tiarella. She states that 3 successive 

 freezings and tha wings "break the colloid structure" of 

 Mnemiopsis, its constituent parts "going into solution," 

 and that the animal "disappears," the disappearance 

 being sudden and definite. For Pennaria, freezing 5 to 7 

 times, or maintaining the temperature at - 10°, produced 

 the same effect. As described, this process, we think, is 

 unique in the literature. 



2. Helminthes. Oliver {Lancet, p. 357, 1910-1) re- 

 ported that larvae of the JwoJi-worm recovered after hav- 

 ing been frozen solid in water and thawed slowly. 



Kjava {Finska Laek. HandL, 55, 101, 1913) showed that 

 plerocercoids of DipliyUohothrium latum were killed when 

 kept for 48 hours at - 9°. 



According to Magath and Essex {J. Prev. Med., 5, 239, 

 1931), all the larvae of Diphyllohothrium latum in 10 

 heavily infected fish {Stizostidion vitreum) were killed 

 when the fish were exposed to -15° for 24 hours. Ten 

 larvae that had been kept in fish at - 10° for 88, 40, and 

 16 hours respectively were fed to each of 3 dogs ; no worms 

 developed. 



Schmidt, Ponomarer and Savellier (1915) studied the 

 resistance of encysted Trichina to cold. They found that 

 a temperature of 0° for 11 days does not affect this para- 

 site, that it can also support -6° for 10 days, that -9° is 

 sometimes but not always fatal, and that -15° to -16° is 

 always lethal. 



