492 A.H. Estabrook 



denly adding a large amount of Worcester's solution (a saturated 

 solution of HgClo in lo per cent formalin). When Paramecia are 

 properly killed by this method no distortion takes place. They 

 were then measured by projecting them with the Edinger projection 

 apparatus, and measuring the image with a millimeter scale. 

 Lenses of such combinations were used that three microns in 

 the object were equal to one millimeter in the projected image. 

 The measurements were then converted into microns by multiply- 

 ing by three. 



GROWTH IN DISTILLED WATER 



Before studying the effects of chemicals as upon growth it is well 

 to examine growth in a fluid containing as small an amount of dis- 

 solved chemicals as possible; that is, distilled water. Any growth 

 taking place in distilled water will evidently not be due to food 

 materials present in the medium nor is it likely to be due to any 

 specific salts, since these are almost lacking. After the nature 

 of growth in distilled water has been determined, the specific 

 effects of substances dissolved in the water can be studied. 



Daniel ('08) showed that if Paramecia are introduced directly 

 from hay infusion (which has a high salt content) into pure dis- 

 tilled water, it is the sudden change that injures them. He also 

 showed that they could be made to live in pure distilled water if 

 they were introduced into it gradually. 



The distilled water used in the experiments was made by Dr. 

 G. F. White of the Johns Hopkins Chemical Laboratory. Ordi- 

 nary laboratory distilled water was redistilled from sulphuric acid 

 and potassium chromate, then distilled from barium hydrate and 

 condensed in block tin. This water gives a conductivity of about 

 2 X lO"". 



Effect of Pure Distilled Water 



In the experiments, one half of a dividing specimen was placed 

 in hay infusion, such as w^as known to be favorable to growth: 

 the other was placed in pure distilled water. Before transferring 



