156 THE QUANTITATIVE METHOD IN BIOLOGY 



less important errors being continually committed, the effects 

 of the regular increase of pipette B (the effects of growth) are 

 disordered according to the rules of chance. 



The 200 portions may be represented by 200 small dots 

 (Fig. 20), the distance between each dot and a horizontal line ot 

 representing the volume of the corresponding portion. 



Fig. 20 represents the observed growth of the property 

 volume (during a period of 199 x 10 = 1990 minutes) deduced 



1 11 ]]I IV V VI VII VIII !X X t 



Fig. 21. — The distance between each small dot and oi is supj)osed to 

 represent the weight of the precipitate in a portion. The thick dots 

 represent the curve of growth (see text) ; ot, time ; 0, origin 



from the measurement of 200 specimens of successive ages, the 

 last specimen (last small dot) being 199x10 = 1990 minutes 

 older than the first one. This total duration may be divided, 

 for instance, into 10 equal intervals, I., II., . . . X. For each 

 interval the mean volume of the corresponding specimens (small 

 dots) may be calculated. Since each interval includes twenty 

 specimens, the positive and negative errors are counterbalanc- 

 ing one another in a certain degree.^ The ten mean values being 

 plotted out in the form of thick dots, it is seen that the latter are 

 situated approximately on a straight line which is the curve of 



^ The result would be, of course, better if the portions were more numerous. 

 (See, on the conclusion drawn from a series of twenty observations, § 93, p. 118.) 



