Tubes must be tested again about every four weeks. Should any error in diagnosis have occurred before this time, and other possible errors have been excluded, then the tubes must be immediately tested for permeability to albumen and for even permeability to peptones.
(2) Serum.—Here we have to deal only with its age, the possibility of an infection, hæmolysis, and the contents of the serum in respect of red blood corpuscles and of other form-elements. (See pp. 173-175-)
(3) The Organ.—This is nearly always the cause of errors in diagnosis. It is nearly always forgotten that, in the arrangement and execution of the experiment, we are dealing with quantitative conditions. Two cases have to be distinguished:—
(a) The Biuret Reaction.—The serum alone does not give off substances which diffuse and produce a biuret reaction; so that, as regards compounds which give a biuret reaction, it must be reckoned as completely indifferent. It is comparatively easy to boil the organ in such a way, that the water in which it was boiled will not give any biuret reaction. If the ninhydrin reaction turns out negative, one can never obtain a biuret reaction. If such an organ be mixed with serum, and the dialysate now gives a positive biuret reaction, then we may be sure that decomposition has taken place. The conditions here are very simple.
