TOXICOLOGY AND PHARMACOLOGY 393 



The study of these forms of life is difficult because of the lack of 

 technical methods for their investigation. Besides dark-field illumi- 

 nation, colloid research has provided two methods which have already 

 led to important advances: these are ultrafiltration and adsorption. 

 By means of the Chamberland filter the solution of virus may be 

 freed from visible bacteria. In order to concentrate the filterable 

 germs and make quantitative tests with them, they may be con- 

 centrated on an ultrafilter, as was done by BETEGH with hog cholera 

 virus, PROWAZEK and GIEMSA with variola; or they may be adsorbed 

 on charcoal or clay (as did GINS with smallpox). 



I believe the colloid investigation of filterable microorganisms will 

 yield valuable results, since they form a transition group to true 

 colloids. A beginning has already been made. Thus ANDRIEWSKY 

 has shown by ultrafiltration that the virus of chicken cholera is 

 smaller than the hemoglobin molecule. 



It has been repeatedly observed that the development of micro- 

 organisms is facilitated by the presence of suspensions or hydrogels. 

 Thus KKZEMIENIEWSKI found that a pure culture of nitrifying bac- 

 teria grew more luxuriantly and bound more nitrogen if earth or 

 humus was added to the culture medium and KASSERER found a 

 similar effect from the addition of colloidal silicates and phosphates 

 of iron and aluminum. According to Ross VAN LENNEP pieces 

 of kidney, meat, cellulose, etc., improve the growth of aneorobic 

 bacteria, yeast and B. coli. We thus see that these microorganisms 

 on purely physical grounds find much more favorable conditions for 

 growth in their natural habitat than in artificial media. In some 

 instances it was possible to determine the reason for this phenomenon. 

 Thus SOHNGEN* and also Ross VAN LENNEP showed that charcoal 

 and some other solids favor the dissipation of carbonic acid which 

 inhibits the growth of yeast. In other instances the suspensions or 

 colloids adsorb oxygen for aerobic bacteria, nitrogen for nitrifying 

 bacteria, or other nutritive ingredients which are then available for 

 growth at the surfaces of the respective substances (literature given 

 by SOHNGEN *) .* H. FREUNDLICH ** mentions the following substances 

 which show slight adsorptive affinity: salts (especially of the baser 

 metals), highly dissociated substances (such as strong acids and bases), 

 aggregations of OH groups (sugar) and the sulpho group. As a 



1 Though it is shown on page 396 that the distribution of phenol between 

 the bodies of the bacteria and their environment occurs as it would in two sol- 

 vents, it does not by any means contradict what has been said here, since a dis- 

 infectant action does not result from adsorption. Disinfection occurs when the 

 disinfectant penetrates the microorganism; the portion which has penetrated 

 may very well comply with HENRY'S law (distribution). 



