EFFECT OF CONJUGATION 283 



nated a and h. It is important to understand that these desig- 

 nations do not imply any characteristic differences, the two 

 letters being assigned arbitrarily and at random to the two mem- 

 bers, in order to make it possible to speak of them separately. 

 But the individual and its progeny to which a given letter is 

 assigned of course retain this designation throughout. The pairs 

 (and split pairs) of any experiment are designated by serial 

 numbers, so that any individual is indicated by a number and 

 a letter; thus 86 signifies the individual b of pair 8. The lines 

 of progeny from a given individual receive the same designation 

 as the parent individual, so that in later stages of the experiment 

 85 signifies the line of progeny derived from the individual b 

 of the pair 8. 



Culture. The isolated individuals were transferred to the 

 concavities of hollow ground glass slides, each concavity con- 

 taining two or three drops of culture fluid. Thick slides with 

 two concavities were found most convenient. At the beginning 

 the animals were usually left for one or two days in water from 

 the dish in which they were found, in order not to disturb the 

 processes of conjugation by the shock of removal to a different 

 fluid. For the later cultivation an infusion of pure Timothy hay 

 was usually employed. This was jnade by boiling one gram of 

 Timothy hay for ten minutes in 100 cc. of tap water, then adding 

 to this infusion, after it was cool, 100 cc. of filtered but unboiled 

 water. Sometimes this filtered water was taken from the parent 

 culture; a procedure that, in some cases, though not in all, works 

 well. The infusion was tried in varying strengths at different 

 times, but all the animals of a given experiment were treated 

 throughout in exactly the same way. The infusion was invariably 

 made up fresh just before it was used. 



In the last experiments tried, it was found that yV per cent 



Horlick's malted milk, as recommended by Peebles ('12), was 



Referable in some respects to the hay infusion, particularl}^ in 



.•iummer. It was found necessary, for the best results, to make 



up this culture fluid fresh each day. 



The animals were transferred to two drops of fresh infusion, 

 on a clean slide ; in some experiments every day, in others every 



