188 MR. H. A. SMITH ON ANIMAL LIFE 



The acidity was now raised to o*oi grm. per litre, and 

 the solution allowed to stand twenty-four hours. The 

 appearance of the solution had not varied to the smallest 

 degree. On further acidification till the amount reached 

 o*oi8 grm. per litre, no difference was observed between 

 the present and the original solution. However, on the 

 further addition of O'ooi grm. per litre (that is, on raising 

 the acidity to 0*019 grm. per litre) a very decided differ- 

 ence was noticeable; all life had become extinct. The 

 change from active life to death was almost instantaneous, 

 and could be most distinctly seen by the microscope. The 

 bodies of the Rotifers, generally so clearly white and 

 transparent, became, immediately on the addition of the 

 acid, of a dull opal-like appearance; and all movement 

 was arrested. The solution remained clear; and the 

 bodies of the Rotifers were seen floating in it, becoming 

 rapidly acted upon by the acid. Even while watching, in 

 the short space of ten minutes they became " shredded." 

 Here, then, the line between life and death is very 

 sharp, much more so than in the observations with 

 sulphuric acid. 



The present experiments extended over the same space 

 of time as those in the former case — eight days from the 

 time of washing air, or four days from time of first ob- 

 servation. 



The same attempts were made as formerly to find the 

 amount of acidity which would prevent life originating, 

 the present results being : — 



Time allowed to stand. Total acidity. Remarks, 



days. grm. per litre. 



5 0-0085 Life abundant. 



26 0*009 No life. 



Thus, then, we see that the addition of 0*0005 g rm « P er 

 litre of hydrochloric acid prevented the origination of life, 



