438 PROTOPLASM 



as it too has been found in milk. It is supplied to the adult by 

 protein foods and is either used in increasing the protein content 

 of the body and repairing protein waste or oxidized for the 

 production of energy and lost as sulphate in the excreta. 



L. G. Wesson suggests the following salt mixture for use in 

 compounding synthetic diets for experimental animals: 



Mixture Grams Mixture Grams 



NaCl 105.0 FeP04 + 4H20 14.7 



KCl 120.0 MnS04 (anhydrous) 0.20 



KH2PO4 310.0 K2Al2(S04)4 + 24H2O 0.09 



Ca3(P04)2 149.0 CUSO4 + 5H2O 0.39 



CaCOa 210.0 NaF 0.57 



MgS04 (anhydrous) 90 . KI . 05 



This mixture supplies the following ions: sodium, potassium, 

 calcium, magnesium, iron, manganese, copper, aluminum, 

 phosphate, sulphate, chlorine, fluorine, iodine. 



It must be remembered that salts supply only the inorganic 

 needs of animals. An organic (carbohydrate, fat, and protein) 

 diet is the first prerequisite for an animal; the salts merely 

 supplement it. (The claim has been made, notably by S. O. Mast, 

 that certain simple animals, such as Chilomonas Paramecium, can 

 exist on a purely inorganic diet.) 



Salt solutions exercise certain influences upon protoplasm 

 because of their osmotic, electric, or other purely physical 

 properties, considered apart from their chemical constitution 

 (it is always very difficult wholly to dissociate the two). Ringer 

 found that sodium chloride used for the continuous perfusion of 

 the heart of the frog removed from the body does not maintain 

 the normal beat. This may be due to the lack of some other 

 salt, essential because of itself alone or because it is needed to 

 counteract a possible "poisonous" effect of the sodium chloride. 

 The osmotic pressure of the solution may also be at fault. This 

 last possibility was taken care of in Ringer's experiments by mak- 

 ing the solution isosmotic with (of the same osmotic value as) 

 blood (which is given by 0.75 per cent sodium chloride). The 

 two other possibilities Ringer proceeded to study. He found 

 that calcium chloride added to the sodium salt caused the heart 

 to renew beating, although diastole (dilation) was imperfect. 

 Calcium augments systole (contraction). Ringer next discovered 

 that potassium has an effect opposite to that of calcium; it 



