532 Professor Percy F. Franhland [Feb. 19, 



more complex than that of any inanimate chemicals which we are 

 accustomed to emj)loy. In a chemically pure substance we believe 

 that one molecule is just like another, and hence we expect perfect 

 uniformity of behaviour in the molecules of such a 2)ure substance 

 under prescribed conditicms. In a pure cultivation of a particular 

 species of a micro-organism, however, we must not expect such rigid 

 uniformity of behaviour from each of the individual organisms 

 making up such a cultivation, for there may be and frequently are 

 great differences amongst them, in fact each member of such a pure 

 culture is endowed with a more or less marked individuality of its 

 own, and these possible variations have to be taken into considera- 

 tion by those who wish to turn their energies to account. In fact, 

 experimenting with micro-organisms partakes rather of the nature of 

 legislating for a community than of directing the inanimate energies 

 of chemical molecules. Thus frequently the past history of a group 

 of micro-organisms has to be taken into account in dealing with 

 them, for their tendencies may have become greatly modified by the 

 experiences of their ancestors. 



Of this I will give you an instance which has recently come under 

 my observation : — 



Here is a bacillus, which has the property of fermenting calcium 

 citrate ; I have found that it can go on exerting this power for 

 years. On submitting this fermenting liquid to plate-cultivation, 

 we obtain the appearances which you see here. 



[Lantern-demonstration of plate-culture of bacillus which fer- 

 ments calcium citrate.] 



If one of these colonies be transferred to a sterile solution of 

 calcium citrate, it invariably fails to set up a fermentation of the 

 latter, the bacillus having thus by mere passage through the gelatin- 

 medium lost its power to produce this effect. If, however, we take 

 another similar colony and put it into a solution of broth containing 

 calcium citrate, fermentation takes place ; on now inoculating from 

 this to a weaker solution of broth containing calcium citrate, this 

 also is put into fermentation, and by proceeding in this manner we 

 may ultimately set up fermentation in a calcium citrate solution which 

 absolutely refused to be fermented when the bacilli were taken 

 directly from the gelatin-plate. 



Phenomena of this kind clearly indicate that there may be around 

 us numerous forms of micro-organisms of the potentiality of which 

 we are still quite ignorant ; thus if we were only acquainted with the 

 bacilli I have just referred to from gelatin cultures we should be 

 quite unaware of their power to excite this fermentation of calcium 

 citrate, which we have only been enabled to bring about by j)ursuing 

 the complicated system of cultivation I have indicated. It is surely 

 exceedingly probable, therefore, that many of the micro-organisms 

 with which we are already acquainted may be possessed of numerous 

 important properties which are lying dormant until brought into 

 activity by suitable cultivation. 



