154 THE QUANTITATIVE METHOD IN BIOLOGY 



means of an exact pipette A and an imperfect pipette B. 

 (See p. 148.) The three series of experiments may be repeated 

 under the following conditions : — 



(i) The successive mixtures are prepared at equal intervals 

 of ten minutes each and marked with a number indicating their 

 order of succession. 



(2) Pipette B is supposed to increase regularly (unknown to 

 the operator) through the whole duration of each series of 

 experiments,^ with such a velocity that the volume indicated 

 by degree 10 is increasing by o-oi c.c. in the course of each 

 interval of ten minutes. I ascribe here to pipette B a property 

 of the living beings — ^namely, growth. 



(3) At the beginning of each of the three series degree 10 of 

 pipette B coincides (unknown to the operator) with a volume 

 of 9 c.c. instead of 10. 



Suppose that in each series 200 portions (mixtures) are pre- 

 pared. In all the portions the already mentioned properties 

 are measured or observed — viz. 



ist Series (fourteenth example) : water + water : property 

 volume. 



2nd Series (fifteenth example) : acid + alkali : property colour 

 (red or blue). 



3rd Series (sixteenth example) : salt a + salt b : property 

 weight of the precipitate. 



is^ Series. — If no errors were committed, volume i (first 

 portion) ^ would be 10 + 9 = 19 c.c. In a similar way — 



200 „ 20-99 ,, 



1 For instance, by an increase of its diameter unperceived by the operator. 



2 Volume 1 is prepared at the moment o. 



