The experiments of Professors Pumpelly and Smyth for the National Board of Health at Washington are extremely interesting and fully corroborate those of Carmichael.

In their first series made to determine whether bacteria or other particulate matter can disentangle themselves from a liquid, water, sewage and putrefied substances were suspended, as shown in Fig. 44, in a bent tube over a sterilized beef infusion in a room where the temperature ranged between 20 and 35 degrees Centr. The flask containing the infusion was closed air tight by a rubber stopper, through which the tube passed, which held the sewage in a small bowl or trap at its lower end. The stoppers contained also a small asbestos filled filter tube. In this form of the experiments the air around the sewage was in a state of rest.