334 DISCOVERY REPORTS 



alkalinity in spring, and that this increase was due to the photosynthetic activity of the 



phytoplankton. 



Atkins (1923ft) has made further studies of the seasonal changes in alkalinity, and has 

 come to the conclusion that " in a general way the pH maxima (alkalinity maxima) may 

 be correlated with the diatom maxima in the early summer and autumn, but no quanti- 

 tative results have as yet been obtained on this point. The alteration in the reaction of 

 the water may be used to make an approximate estimation of the total crop of algal 



plankton". 



Many years ago Loeb (1906) showed that Copepoda became positively phototropic 

 by reducing the alkalinity of the environment. More recently Fox (1925) has shown 

 that both changes in light and^H can independently bring about the vertical migration 

 of Paramecium. 



It is well known that very small changes in hydrogen-ion concentrations have a 

 marked effect upon the animal organism. Professor Lloyd Hopwood, in his article on 

 "Physics in Medicine" in the recent edition of the Encyclopedia Britannica, writes as 

 follows : 



An alteration in acidity is the causative factor in the regulation of respiration, the activity of muscle, 

 and the excitability of nerve, and plays an important part in regulating excretion and secretion. 



The powerful effects of variation in hydrogen-ion concentrations on physiological processes require 

 the existence of mechanisms for the prevention of considerable changes of this kind. One of the 

 main functions of the blood is to provide this. It can itself withstand the addition of relatively con- 

 siderable amounts of free acid or free alkali without much change in its reaction, largely owing to the 

 presence of carbonates and phosphates. The electrolytic dissociation theory provides the only satis- 

 factory explanation of this. 



He is of course referring to the terrestrial vertebrate. The planktonic organism is 

 bathed in a great medium— the sea— and even if we imagine it possible for the organism 

 to regulate to some extent the alkalinity of this medium in its immediate vicinity, we 

 cannot imagine that it could counteract the larger variations that may at times occur and 

 be harmful to it. We might expect that it would if possible move within the medium to 

 a region more congenial to it. 



Shelford and Powers in 191 5 J showed how sensitive fish may be to small changes in 

 pH, and Powers (1921, 1922) traced the limits of pU within which various fish were 

 found in Puget Sound. He only once found herring in water with a pH above 7-9 and 

 never found them in water below pll 771. Atkins (1923ft) however writes: 



. . .While such preferences and variations may be observed in estuarine waters, in the sea around 

 this coast, the water is, as demonstrated by the figures already given, very uniform in alkalinity, and 

 during winter not far from/>H 8-14, yet herring are at times caught in great quantity, as well as other 

 fish. One can only conclude that under such conditions the hydrogen ion concentration of the water 

 can be of no importance in determining the movements of fish.. . . 



Saunders (1924) has described the swarming of the protozoan Spirostomum induced 

 by increased alkalinity due to the photosynthesis of algae. We have ourselves described 

 on p. 210 the swarming of immature Euphausia superba, a close swarming apparently 



1 Quoted by Atkins (1923/1). 



