98 INFLUENCE OF VARIOUS AGENCIES 



the preservation of a normal physiological condition of the body ; 

 in the formation and action of pigment cells ; in the powerful 

 effect upon epidermal cells of sunlight apart from the heating 

 effect ; in the probable effects of insufficient sunlight, in producing 

 the cretinism found in the inhabitants of certain valleys ; in the 

 effects of light under certain conditions in producing ophthalmia. 

 Here may be mentioned also the action of various other forms 

 of radiant energy upon living cells, such as the X rays and Finsen 

 rays, and the radiations of radium, which act as such powerful 

 stimulants upon living cells. 



Action of Acids and Alkalies and of Neutral Salts upon Enzymes 

 and Living Cells. In considering the value of food-stuffs such as 

 proteids, carbohydrates, and fats as sources of energy to the body, 

 we are too apt to forget that energy is not the only thing required, 

 and that in order to use this energy, the integrity of the mechanism 

 for its conversion or transformation, viz. the living cell, is no less 

 important. For the preservation of this integrity, the simple 

 inorganic salts, and a due proportionality between acid and alkali, 

 are no less important, and such simple substances are no less 

 indispensable than the organic food-stuffs. It has been shown 

 by Ringer and others that normal physiological activity is not 

 possible in the presence of the organic or energy-yielding con- 

 stituents alone, that these may be present in abundance, and 

 yet the tissue be entirely incapable of functionating unless it is 

 also fed with certain inorganic constituents. Ringer further 

 showed in the case of the frog's heart that there must be a certain 

 balance maintained between the various inorganic constituents, 

 that sodium chloride alone could not maintain the activity, but 

 that it was necessary to have present both potassium and calcium 

 in certain balanced proportions. Working on the basis of his 

 experiments, he devised " Ringer's solution," containing these 

 substances in the proper concentrations for the preservation of 

 physiological activity, which has since, in various modifications, 

 been employed by most subsequent workers on the subject. 



The work begun by Ringer has been continued by many 

 workers, and extended into observation of the effects of variation 

 of the inorganic salts, and of acids and alkalies, not only upon 

 a maintenance of physiological activity, which was the problem 

 chiefly studied by Ringer, but also of the effects upon rapidity 

 of cell growth and division and of reproduction. 



