152 ILLINOIS STATE ACADEMY OF SCIENCE 



tially a de-solution effect brought about purely by physi- 

 cal causes, and any bacterial or biological action is defi- 

 nitely ancillary." Dr. Remsen is quoted as saying that 

 the value, of a theory is to be judged by the experimental 

 work which it stimulates. Judged on this basis . the 

 Hampton doctrine does not make much of a showing. 



The other theory is that of Dunbar, with perhaps 

 some modifications, and holds that the results are 

 brought about largely by biological catalysts which pro- 

 duce biochemical reactions. 



If one examines particles of activated sludge under 

 the microscope he is impressed immediately with the 

 fact that there is practically no adsorbed, precipitated 

 or coagulated amorphous matter in these sludge par- 

 ticles, but that they are composed entirely of active 

 growing microscopic organisms of varieties ranging 

 from true bacteria up through the giant bacteria, with 

 occasionally molds and yeasts, and including as well, a 

 variety of free swimming and attached protozoa. These 

 communities of microorganisms must obtain food, and 

 this food must be supplied from the colloidal and dis- 

 solved matter and salts in the sewage. From what we 

 know of the metabolism of microorganisms it is prob- 

 able that the unicellular forms are absorbing through 

 their membrane such soluble forms of organic matter as 

 are able to pass through this membrane, and that they 

 are also secreting enzymes which are capable of pep- 

 tizing or liquefying colloidal particles too large to be di- 

 rectly absorbed. Protozoa, on the other hand, can easily 

 be seen to approach and ingest visible particles of or- 

 ganic matter. This biological theory of the action of 

 activated sludge might be summarized and emphasized 

 by proposing what seems to be a rather striking analogy, 

 namely, that the purification of sewage effected by 

 microscopic communities appearing as floes is entirely 

 similar to that of disposal of garbage by feeding it to 

 hogs. It does not seem probable. that adsorption of col- 

 loids or mechanical precipitation plays any greater part 

 in the metabolism of microorganisms than they do in 

 +he digestion of the larger animals. One serious objec- 

 tion to the colloidal theory of coagulation is that the 



