Note 55 — COMPARATIVE EXPERIMENTS.

This again is a most instructive experiment when compared with Nos. XVI. and XX., in which portions of the same infusion were employed. The results in No. IX. would lead us to believe that a vegetable infusion which does not ferment, does, nevertheless, undergo some changes in molecular composition, and this notion seems to derive confirmation from the present experiment. Some of the same solution which has been kept for a time (twelve days) from contact with atmospheric particles, subsequently, even when fully exposed to the air, undergoes no apparent change for six days, and then, instead of becoming filled with Bacteria, swarms only with Torulæ. Yet the infusion in this condition was perfectly capable of nourishing Bacteria, as I subsequently proved by inoculating it. Why then was it not inoculated by the living Bacteria, with which the air is thought by some to be teeming?