148 GENERAL BIOLOGY 



Paramecium probably never encysts and a hay infusion 

 made as sometimes directed, but not inoculated from some 

 source containing the animals, will not give rise to para- 

 mecia. The culture must be inoculated from an old culture, 

 or the animals must be introduced from outside sources. 



To kill Paramecium hot Worcester's fluid is probably the 

 best. A round bottomed vial is filled one-third full from a 

 good culture, with as many of the animals and as little fluid 

 as possible. Fill the vial to the top with hot Worcester's 

 fluid and allow to stand fifteen minutes, during which time 

 the animals will settle to the bottom. With a pipette draw 

 off as much of the killing fluid as possible and add water to 

 wash, using several changes and stirring up the mass of 

 paramecia as little as possible. Stain in hematoxylin 

 rather heavily, destain with weak acid, or acid alcohol, until 

 the color is very faint except in the nucleus. W T ash in water, 

 dehydrate, clear and mount on a slide in balsam. Support 

 the cover glass to prevent crushing the animals. 



Vorticella. If sticks, leaves, and pond weeds are placed 

 in a jar and allowed to stand a day or two a scum will form 

 on the water, and in this scum Vorticella will often be abun- 

 dant. In such fresh cultures large specimens are usually 

 found. The methods used for continuing Paramecium 

 cultures will be fairly successful for Vorticella. Similar 

 metiiods of killing and staining may be used but are not 

 very successful, on account of the contraction which usually 

 takes place in Vorticella. 



Hydra. In ponds, swamps, and slow moving streams 

 covered with "duck-weed'"' (Lemna) green hydra will often 

 be abundant in spring and summer. Brown hydra is more 

 often found in larger ponds and lakes on Sagittaria and pond- 

 lily leaves. Place the plants, in both cases, in jars and set 

 in a bright place, but not in the direct sunlight. Within a 



