1 90S 



JENNINGS— HEREDITY IN PROTOZOA. 489 



hay infusion, E died at once, c after a day or two; D multiplied slowly, then 

 died in the course of a week or so, while g and i throve and multiplied. 



It was therefore necessary to bring the different lines gradually into the 

 new fluid, by mixing some of it with the fluid in which they lived, increasing 

 the proportion of new fluid at intervals. This was found to be a very deli- 

 cate undertaking. Certain of the lines would thrive for a time, under this 

 procedure, then would begin to degenerate; in this way much time was lost. 

 Finally, however, the different sets were induced to thrive in the same hay 

 infusion. 



Procedure Necessary for Making the Conditions Identical for Different 

 Lines. — The procedure followed, in order to be certain that the cultural con- 

 ditions were the same for all, was as follows : From each race ten typical 

 individuals were selected. These were mixed with gradually increasing 

 amounts of hay infusion, in the way just set forth — while at the same time 

 of course they multiplied in number. After they had all gotten accustomed 

 to the infusion, it was necessary to take measures to assure the identity of 

 the solutions in which the different sets were living. For this it is not 

 sufficient merely to transport the individuals to definite quantities of the same 

 nutritive solution. For up to this point each set has been living in a solution 

 which has received an admixture of the original culture for that set. Now, 

 these different original cultures contained different kinds of bacteria. On 

 transferring the infusoria to the hay infusion, they of course carried some of 

 their own bacteria. By repeated changes the number of bacteria introduced 

 could be much reduced. Nevertheless different kinds were brought in in 

 different cases, so that we still have the different lines in cultures of diverse 

 bacteria. From this fact naturally diverse chemical properties may develop 

 in the different cultures, though the basic nutritive solution is the same. 

 These diverse chemical properties would of course modify the organisms, 

 making it impossible to compare them with regard to inherited size. To 

 make the conditions of existence the same, it is not sufficient to attend 

 merely to the basic fluid; tlie bacteria in the fluid must also be the same. 

 This is a principle of wide practical importance in all experimental work wi+h 

 such infusoria. It is not a mere theoretical requirement ; death frequently 

 results from the introduction of a certain kind of bacteria into a certain 

 culture, while another culture of identically the same fluid flourishes, be- 

 cause the bacterial infection is different. 



This requirement was met in the following way: After the different 

 sets had become acclimatized to the same hay infusion, ten of each were 

 removed with a fine capillary pipette, and washed twice in fresh hay in- 

 fusion. The second washing of the different sets was done in the same mass 

 of fluid, — a small watch-glass full. The different sets might of course each 

 carry with them a few of the bacteria characteristic of their original culture. 

 After all had been washed in the same mass of fluid, this fluid would of 

 course be infected with bacteria from all the different sets. Now, after the 

 washing was finished, a definite quantity of this fluid in which all had been 

 washed ivas added to the final culture fluid for each lot. 



Thus each lot of ten is in the same quantity of the same nutritive fluid, 



PROC. AMER. PHIL. SOC. XLVII. I90 FF, PRINTED JANUARY 12, I9O9. 



