Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/219

 before the tube is filled 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 compounds that produce coloration with ninhydrin. Only from a certain concentration onwards is the coloration possible; and this limit we designate by the number 1. Then, to give an example, the cases quoted in the annexed table are possible:—