NUCLEO-CYTOPLASMIC RELATION OF OXYTRICHA 9 



were continued by the daily isolation of a specimen from each 

 which was placed in fresh culture medium on a clean slide. The 

 accompanying graph (fig. 1) shows the daily rate of division of all 

 four lines averaged together and this again averaged for each 

 ten-day period of the life of the culture. 



Infusions of hay or grass were used to the exclusion of all 

 other culture media except at certain periods of acute physiologi- 

 cal depression. These exceptions are of no interest for the pres- 

 ent problem because the animals preserved from such periods 

 have been excluded from the series measured ; for example during 

 periods 21 and 22 when beef extract was employed in an endeavor 

 to rejuvenate the race. The great rise in the rate of reproduc- 

 tion which occurred later was attributed to this temporary en- 

 vironmental change. The culture was subjected to the ordinary 

 room temperatures throughout the work, but such variations as 

 occurred are unimportant as the mean temperature during parts 

 A, B, C and D is essentially the same and produces an error 

 which is negligible, when the length of the periods and the num- 

 ber of specimens under consideration is taken into account. 



As the present study is based entirely upon measurements of 

 mounted specimens the following statement of the methods em- 

 ployed in preservation is important: 



The specimen to be preserved is isolated by means of a fine-pointed 

 pipet on a clean depression slide .... with as little of the 

 culture medium as possible. To this is added three or four drops of 

 bichlorid of mercury in saturated solution with 5 per cent of glacial 

 acetic acid. After about five minutes the specimen is transferred to 

 another slide and a few drops of 75 per cent alcohol is added. A slide 

 is now smeared with a trace of egg-albumin and the specimen is taken 

 from the 75 per cent alcohol and gently spurted onto the albumin. 

 After a short time, when the alcohol has coagulated the albumin, the 

 slide with the specimen adhering to it is transferred to a jar of 75 per 

 cent alcohol and is thereafter treated by the ordinary slide method. 

 For staining, Ranvier's picrocarmin was used .... Clearing 

 was 'done with xylol, and damar was used in mounting. 



All the specimens were fixed, stained and mounted in exactly 

 the same way so that alterations due to shrinkage should be 

 approximately the same. Some two hundred slides were made 



