406 COLLOIDS IN BIOLOGY AND MEDICINE 



From the length of time required to kill the germs and from the con- 

 centration of the disinfectant solution we may judge the strength of 

 the disinfectant action. 



From the standpoint of the colloid chemist the silk thread pro- 

 cedure contains a serious error of method. Even at present on 

 account of its apparent simplicity this method is frequently em- 

 ployed. We know from practical experience that silk is a very 

 powerful adsorbent. The investigations of W. SCHELLENS * on the 

 relation of silk to sublimate is of interest in this connection. He 

 shook 1 gm. silk with 50 c.c. of 1 per cent sublimate solution and 

 then determined how much mercury was present both in the re- 

 maining fluid, and in the silk after it had been washed many times. 

 He found that the silk had taken up 6.04 per cent of its weight of 

 metallic mercury but had fixed only 1.9 per cent. We thus see that 

 silk retains very considerable quantities of sublimate. Similar re- 

 sults were obtained by W. SCHELLENS for ferric chlorid, ferric acetate, 

 several mercuric salts, lead nitrate, etc. From this we must con- 

 clude that silk is not a suitable germ carrier for disinfection experi- 

 ments, since as the result of adsorption (no action can be ascribed 

 to the " fixed" mercury, etc.) it retains too much disinfectant; on 

 this account the germ cannot escape from the disinfectant, and ac- 

 cordingly we are only given information relative to inhibition of 

 development and not concerning the lethal action. PAUL and 

 KRONIG chose, as germ carriers, marbles because the disinfectant 

 can barely adhere to them by adsorption. H. BECHHOLD and P. 

 EHRLICH,* as well as H. BECHHOLD, * 9 in their experiments on lethal 

 action completely discarded germ carriers; they prepared bac- 

 terial cultures on agar, which they covered with the disinfectant 

 fluid. After removing the disinfectant, they washed the culture 

 twice with physiological salt solution (which is finally made very 

 faintly alkaline) and then transplanted the culture to a new medium 

 (agar). On account of the thickness of the culture, very great 

 demands are made upon the disinfectant by this method, but no 

 germ carrier whatever is transferred to the new culture medium, 

 and the method thus completely avoids the source of error men- 

 tioned above. 



The experiments on the disinfectant action of formaldehyd gave 

 such contradictory results, because the great adsorption of formalde- 

 hyd by silk was ignored, as was pointed out, especially by SCHUM- 

 BERG.* 



In order to annul the adsorptive action of germs and germ carriers 

 in disinfection experiments, an attempt was made to render the 

 disinfectant inactive by chemical means, as it was found impossible 



