INTRODUCTION 9 



function of t, we plot y 2 as a function of t, then the 

 j^-curve is a straight line, running through the 

 origin, y = o, t = o, and we easily see that the y 2 - 

 value does not approach to a limit. In this case we 

 might just as well have tabulated jj/asa function of 

 the square root of t,y = ad~t and have obtained a 

 straight line. In the figure 7 representing Schutz's 

 rule, some experiments of E. Schutz are indicated 

 by points. Here the quantity x digested in a given 

 time is represented as a function of the square root, 

 s/q, of the quantity, q, of pepsin used for the 

 digestion. 



In general if we have a formula expressing a 

 connection between two quantities of which we 

 change the one u experimentally, while we observe 

 the corresponding magnitude of the other, z y which 

 formula may be 



f(z) = K . P (u) + 6, 



we shall always be able to illustrate this formula 

 graphically by a straight line by choosing y =f(z) 

 and x = p(u), for then we have the linear formula 



y = K . x + b. 



But in most cases it is preferred to plot z as a 

 function yjr(u) of u and to draw a curve through the 

 plotted points, indicating the values actually ob- 

 served by means of points or crosses. This 

 method is preferred as soon as the functions f(z) 

 or p{tt) are at all complicated, so that we are not 



