STUDIES ON THE LIFE CYCLE OF PARAMECIUM. 289 



periods has been plotted (cf. Figs, i, 2 and 3). Permanent prep- 

 arations have been preserved at various periods in the life history 

 for the purpose of studying the cytoplasmic and nuclear changes, 

 if present. 



The culture was carried on at the Thompson Biological 

 Laboratory of Williams College, Williamstown, Mass., during 

 May and June, 1907 ; at the Marine Biological Laboratory, 

 Woods Holl, Mass., during July and August, 1907 and 1908 ; 

 and at the Sheffield Biological Laboratory of Yale University, 

 New Haven, Conn., from September, 1907, to July, 1908, and 

 from September, 1908, to the present time (June, 1909). 



During the first nine months of the work the culture medium 

 was made of hay or grass ; but, except during certain periods in 

 which the culture was employed as a control for special experi- 

 ments, 1 the infusion was made with hay from various localities, 

 and different proportions of hay and water were used almost 

 daily. Water from different sources was employed. The tem- 

 perature of the infusion was always raised to the boiling point. 

 In some cases the infusion was used as soon as it had again at- 



o 



tained the room temperature ; in others, it was allowed to stand 

 for twenty-four hours before it was employed. 



From February, 1908, to the present time, June, 1909, how- 

 ever, a more varied culture medium was employed. Paramecium 

 will thrive in nearly any infusion which may be made from materials 

 collected in ponds and swamps, and therefore, in an endeavor to 

 supply as far as possible all the elements which may be en- 

 countered in the usual habitat of the organism, water was taken 

 from ponds, laboratory aquaria, etc., together with their animal 

 and plant life. In other words, no definite method was used in 

 selecting the material, but it was simply collected at random from 

 what might be the abode of infusoria, and thoroughly boiled. 

 Probably the only condition present in the life of this culture 

 which could not be encountered by a wild Paramecium was that 

 the water had been boiled, but this was essential in the experi- 

 ments in order to obviate the possibility of the contamination of 

 the culture by an active or encysted wild specimen. Conjuga- 

 tion was impossible in the direct lines of the culture on account 

 of the frequent isolations and change of medium. 



'Woodruff ('08'). 



