532 ,, WALDO SHUMWAY 



then isolated to establish the several lines required. All the 

 customary precautions against contamination were observed, and 

 every attempt made to keep the control and experimental lines 

 under conditions exactly similar except for the kind of culture 

 medium employed. All the watch glasses were stacked in a 

 single large moist chamber and the number of Paramaecia in 

 each was ascertained at the same time. 



The cultures were carefully examined for monstrosities and 

 the later history of many of these followed. In cases where a 

 single individual required a closer study than could be obtained 

 with a binocular or the lower power of the microscope, the fol- 

 lowing procedure was adopted. A ring of vaseline was turned 

 on a slide, the individual in question was placed in a minute 

 drop on a coverslip, the drop drained off with a fine capillary 

 tube until there was barely enough left for the individual to 

 move, the coverslip was then inverted upon the ringed slide and 

 the individual could be studied under high power for a consider- 

 able time and finally returned to the watchglass. After this 

 technique was perfected, no ill-effects were produced on the 

 Paramaecia so treated. Permanent preparations were made 

 from time to time by fixing in Bouin's fluid (picro-aceto-formol) 

 and staining with Delafield's haematoxylin according to the 

 following formula, for which I am indebted to my friend Professor 

 Haughwout : 



Delafield's haematoxylin cone. aq. sol 9 cc. 



Glacial acetic acid 1 cc. 



Distilled water 90 cc. 



Chloral hydrate 5 gr. 



HISTORY OF THE RACES 



The life history of the three races of Paramaecia which have 

 been studied are summarized in the following paragraphs. 



Race A. Paramaecium aurelia. Descended from an indi- 

 vidual isolated March 12, 1913, fromi a mass culture which had 

 been maintained in the Zoological Laboratory at Columbia Uni- 

 versity for several months. This r.ace was kept in pedigreed cul- 

 ture until December 20, 1913, when it died in a typical depres- 



