84 SPIRAL TWIST AXD OPT. ACTTTITY 



next the morpliological dissymmetry of an animal which, 

 in the natural classification, stands far from the bacteria, 

 namely, the land snail, Fruticicola lantzi. In this animal 

 the typical individuals are dextrally spiralled as is the 

 case in the majority of species of snails. Numerous ob- 

 servations have led to the conclusion that, in snails, the 

 sinistrally twisted individuals are ecologically weaker 

 than the dextral forms. In joint occurrence of the two 

 forms the sinistral ones often disappear in a rather 

 short time. Zvetkov (1938) has recently shown, in a 

 study of the distribution of Fruticicola lantzi in Middle 

 Asia, that most of the populations consist of typical 

 forms, dextrally spiralled. Populations consisting al- 

 most exclusively of inverse, sinistrally spiralled forms 

 were found only in some districts separated from the re- 

 maining area by mountain barriers. Such isolated col- 

 onies of inverse forms in both bacteria and hermaphro- 

 ditic molluscs, it is thought, have originated from a sin- 

 gle inverted ancestor. 



I-. Some Physiological Properties of the Dextral and 

 the Sinistral Strains of BaciUus mycoides. a. A c t i o n 

 of temperature. Recent experiments made by 

 Gause (1939) have shown that there is a ditference in the 

 action of temperature on the growth of the dextral and 

 on that of the sinistral strains of Bacillus mycoides. 

 Three series of experiments were performed as follows : 

 A small quantity of inoculating material was placed in the 

 center of the Petri dish, on agar, in the form of a circle 

 0.5 mm. in diameter. Twenty hours after growth had 

 started the diameter of the colony was about 6 mm. at 

 20° C and about 25 mm. at 32° C. Taking then the diam- 

 eter of colonies, either dextral or sinistral, growing at 

 20° C, as a unit, curves of growth in terms of temperature 

 were constructed. Such curves are represented in Figure 

 6. If the rate of growth of the usual sinistral strain is 

 normal, the inverted dextral strain presents the jdIic- 

 nomenon of ''heat injury." 



