38 THE AMERICAN MONTHLY [Feb., 



are watched every two or three hours, and as the cells 

 propagate and small colonies appear in the gelatine after 

 a couple of days, the surroundings of the colonies should 

 be watched, and the aspects of the plate constantly be 

 compared with the sketch in the notebook. If a colony 

 is shaped very irregularly, or if two colonies grow into 

 each other, they are discarded from the sketch. When 

 the colonies have reached the size of a moderate pin's- 

 head they are ready to be transferred into beer-wort. 



The pure culture thus obtained is an absolute pure cul- 

 ture, because it originated from individual cells the de- 

 velopment of which were directly seen. Thus we know 

 that every colony in the places marked o came from one 

 cell. As we had a mixture in our sample, we may ex- 

 pect that the colonies represent the species in the sam- 

 ple, and that they have developed and will develope in 

 accordance with the specific nature of the mother cells. 



When the colonies have reached the size mentioned 

 above, the moist chamber is again taken into the culture 

 box and a number of beer-wort flasks are likewise put 

 in. The chamber is now loosened from the slide, sam- 

 ples from each of the small colonies in the gelatine have 

 then to be carried into wort-flasks. For this purpose a 

 number of small infection needles should have been 

 made by cutting pieces of a platinum or aluminum wire, 

 each about one-fourth inch long. One of these small 

 needles is grasped with a forceps and dipped into one 

 of the small colonies, then it is dropped in one of the 

 flasks and left there. In the same way the rest of the colo- 

 nies are transferred and when what can be used have been 

 disposed of, so that each flask contains a representation 

 from each colony, the flasks are numbered and placed in 



*The development of the individual cells v?as first studied by E. Mitcherlich. 

 See Knapp, Cheniische Technologic 11, 1847, p. 273; ScJiuhe, Chemie fur 

 Landwirthe II, 2, p. 120, 1860, and Report of the (U. S.) Commissioner of 

 Agriculture for the year 1864, p. 517. 



