194 



SOURCES OF ERROR (IN THE PROCESS) 



before the tube is tilled with it. During storage 

 in the incubator no evaporation must take place. 

 Further, when boiling the actual samples, uneven 

 ebullition must not be allowed. An example may 

 help us to make these conditions clear. We will 

 assume that twelve experiments have been made with 

 serum obtained from non-pregnant individuals, and 

 that the serum has in every case given negative 

 results. We conclude that none of the dialysates 

 have attained the necessary concentration in com- 

 pounds that produce coloration with ninhydrin. Only 

 from a certain concentration onwards is the coloration 

 possible ; and this limit we designate by the number T . 

 Then, to give an example, the cases quoted in the 

 annexed table are possible : 



