56 PHYSICAL CHEMISTRY IN MEDICINE. 



lation brought about through electrolytes does not occur 

 if such non- electrolytes as urea or sugar are present; in 

 fact, an already existing coagulum is made to go back 

 into solution when these substances are subsequently 

 added. If thin layers of gelatine spread upon slides are 

 introduced for fifteen minutes into a 0.3 per cent, chromic 

 acid solution kept at an even temperature of about 23 C., 

 the beautiful coagulation structures are produced which 

 BUTSCHLI has described and pictured. As soon, how- 

 ever, as urea is added to the chromic acid solution in the 

 concentration of i.o molecular, the gelatine does not 

 become opaque, and a formation of structure as described 

 above does not take place, even when everything else in 

 the experiment is arranged as before. The gelatine 

 remains clear, and examination with even the highest 

 powers of the microscope shows it to be homogeneous. 

 Urea in the concentration of 0.25 molecular is without 

 effect, while concentrations above 2.0 molecular lead to 

 excessive swelling and solution of the layer of colloidal 

 material. That we are dealing in this experiment not 

 with the inhibiting effects of urea upon gelation, but 

 with its anti-coagulating effects, is shown by the follow- 

 ing. Chlorides cause an excessive swelling and prevent 

 gelation in the same way as urea, a 2.0 molecular sodium 

 chloride solution being equal to a i.o molecular urea 

 solution. Yet chlorides have as electrolytes no inhibiting 

 effect upon coagulation. Corresponding with these facts, 

 it is found that an addition of sodium chloride to the 

 chromic acid solution equivalent in effect to an adequate 

 amount of urea does not at all prevent the formation of 

 the typical coagulation structures in the gelatine prep- 

 arations. These experiments prove definitely that in the 



