l62 PREPARATION OF THE SUBSTRATES 



intensity of the blue coloration is made in each 

 case. It is soon found that a particular intensity 

 prevails. All the tests which show a greater or 

 smaller intensity than this are carefully noted, and 

 the tubes from which the dialysates in question were 

 obtained are rejected. In this case, too, it is neces- 

 sary to be very accurate, otherwise the actual experi- 

 ments may easily lead to deceptive results. Thus it 

 may happen that serum alone, and serum added to 

 a given organ, contain diffusible compounds which 

 react with ninhydrin with precisely equal difficulty ; 

 yet on testing the dialysate in the experiment serum + 

 organ, we may get a positive reaction, because the 

 tube was more permeable to decomposites of albumen 

 than the tube used as a control. 



The tubes that are equally permeable in this respect 

 are now carefully rinsed, then plunged into boiling 

 water for thirty seconds, and finally brought into a 

 sterilized flask. Sterilized water is added, together 

 with an equal quantity of toluol, the fluid being 

 calculated to fill the flask exactly. The tubes are 

 now ready for use. They are taken out of the flask 

 with sterilized forceps and must, if possible, not come 

 into any contact with the fingers during all the 

 manipulations. 



Preparation of the Substrates (Organs'). As material 

 for these tests we use either an albuminous body or 

 else a mixture of these bodies e.g., an organ. The 



