PETERS. — METABOLISM AND DIVISION IN PROTOZOA. 507 



due to Hamburger, and was used successfully by him for the demonstra- 

 tion of permeability in blood corpuscles. 



In the selection of a mediinu two considerations were important. 

 First, the medium must be favorable to the physiological processes of 

 the animal. Previous experiments indicate that of all one-salt media 

 calcic chloride would best meet the requirement. Secondly, the solution 

 of calcic chloride must be as nearly as possible isotonic with the native 

 culture medium from which the animals originate. How to obtain the 

 osmotic value of culture liquids was a question of some difficulty. From 

 conductivity measurements it was possible to infer that their salt-content 

 was so low as to render most methods uncertain in result. After some 

 consideration the following approximate, but for our purpose sufficiently 

 accurate, method was adopted. It was determined what concentration 

 of calcic chloride had the same conductivity as the culture liquid, and the 

 former was then regarded as the osmotic equivalent of the culture medium. 

 When the culture was started it had the following composition, the salt 

 being dissolved in tap-water. 



Na2HP04 00050 m. 



KNO3 00005 m. 



KCl 00005 m. 



FeCla calculated 000005 m. 



To this had been added some hay, some leaves, and some aqueous ex- 

 tract of barley. The effect of these additions is to make the medium 

 consist of a miscellaneous mixture of physiological salts. Exactly which 

 of these are present and in what proportions is of course unknown. The 

 method by measuring the depression of the freezing point is especially 

 applicable in such cases, but here this value would have been too small 

 to be reliable. As is well known, the coefficient of dissociation, i, of a 

 salt solution in relation to its equivalent conductivity, A, is expressed by 



A 

 the equation i = 1 + (^' — \) a and a := ^—. In these formulae i is 



''K T l^A 



the coefficient of dissociation, k is the number of ions into which the salt 

 splits, a is the coefficient of activity of Arrhenius, Aj, is the equivalent 

 conductivity at the concentration v, Ij^ and /^ are the velocities respec- 

 tively of the kation K and anion A. But a may be found with sufficient 

 accuracy for our purpose by_ taking the ratio of A at the given concen- 

 tration, represented by A„, to A at or nearly at infinite dilution, repre- 

 sented by Ado , that is a = — ^. For a number of physiological salts the 



