1334 PROCEEDINGS OP THE ACADEMY OF [1886. 



liffht brown from coloring matter contained in the potato, which 

 does not, however, materially interfere with observations on the 

 growth of bacteria in it. Iodine gives a blue coloration to this 

 liquid, showing that it contains starch, probably in the form of 

 amylon. Another equally good culture fluid is made by treating 

 corn (maize) meal in a similar manner. The solution is colorless, 

 but it is very apt to throw down a troublesome sediment, which 

 makes it less desirable to use than the potato solution. 



Test-tube or flask cultures with these liquids, when kept at a 

 temperature of 25 to 30C., usually show some turbidity in 

 twenty-four hours after being infected, and if the growth is very 

 rapid, bubbles of gas (CO2) will be given oflf, which collect at the 

 surface into a slight froth. In forty-eight hours the liquid has 

 become thoroughly turbid. By this time a thin whitish pellicle 

 has formed on the surface, which does not increase much in thick- 

 ness up to the end of active growth, and rarely becomes wrinkled. 

 With the formation of the pellicle, a sediment gathers at the bot- 

 tom of the liquid, often a centimeter in depth, but which is so 

 light that it only apparently diflfers from the liquid above by being 

 whiter. In the course of some weeks this sediment will mostly 

 gather upon the bottom of the vessel. No difierence has been 

 observed in the appearance of the bacteria taken from diflferent 

 parts of the culture. Those imbedded in the pellicle are not 

 ari'anged in any recognizable order. 



In proportion as liquids are less suitable to the growth of 

 the organism, the visible changes are less. The pellicle may not 

 be formed, and there may be no turbidity, but if any growth at 

 all takes place there will be some evidence of it by formation of 

 a slight sediment. But the occurrence of a precipitate does not 

 necessarily imply growth, for it not infrequently separates from 

 a liquid containing organic matter, although remaining perfectly 

 sterile. 



An infusion of hay, and also of dead, partly decomposed 

 grass from a marsh, gave nearly a normal growth of blight 

 bacteria, but the cells were considerably more refractive than 

 usual. 



A solution of starch, having one part of starch to fifty of 

 water, gave but a slight growth of highly refractive bacteria, 

 without a pellicle, turbidity, or zooglosa. A strong decoction of 

 old barnyard manure acted in the same manner. A solution of 



