26O RALPH S. LILLIE AND EARL N. JOHNSTON. 



varying in width from 20 to 30 microns. The direction and 

 arrangement of the striations depend on the manner in which 

 the growth has taken place. On the symmetrical structures 

 the striations are regular and equidistant. On the whole these 

 precipitation-formations bear a very decided resemblance to 

 group of small shells. 



Rhythmical movements similar to those observed in these 

 precipitation-structures are met with in various other inorganic 

 processes. Periodicity in purely chemical reactions and in the 

 formation of osmotic growths, as well as in the growth and de- 

 velopment of organic structures, has long been known. One of 

 the best examples of chemical periodicity is seen in the so-called 

 Liesegang rings, 1 which are formed by a diffusion-process asso- 

 ciated with regular periodic precipitations. Leduc, 2 in his book 

 "Mechanism of Life," gives a full chapter to periodicity in 

 chemical and other phenomena. He describes certain osmotic 

 structures as having rhythmic motion and as growing period- 

 ically. 3 In Child's book, "Senescence and Rejuvenescence," 

 considerable space is given to the subject of periodicity in or- 

 ganisms. 4 In this discussion he shows that the growth of an 

 organic structure is not an even, uninterrupted development, 

 but is a largely periodic phenomenon. Another interesting and 

 curious phenomenon is the periodic catalysis of hydrogen peroxide 

 by mercury, as described by Bredig. 5 The liberation of gas in 

 the catalytic action takes place intermittently and may continue 

 at regular intervals for an hour or more. An electrical current 

 of action is also produced resembling that produced in the rhyth- 

 mic contraction of the heart, and can be registered in the usual 

 manner by a string galvanometer. A1J of these purely chemical 

 and physical phenomena aie significant in that they point the 

 way to a better understanding of the phenomena of rhythm 

 and periodicity in living beings. 



1 Cf. Liesegang, " Beitrage zu einer Kolloidchemie des Lebens," Dresden, 1909; 

 Stansfield, "Retarded Diffusion and Rhythmical Precipitation," Amer. Joitrn. 

 Set., 1917, Vol. 43, p. i. 



2 Leduc loc. cit., pp. 67-77. 



3 Leduc, loc. cit., p. 156. 



4 Child, loc. cit., pp. 187-193. 



6 Cf. Bredig and Wilke, "Erregung und Beeinflussung katalytischer Pulsationen 

 durch elektrische Strome," Biochem. Zeitscher., 1908, Vol. n, p. 67. 



