KOCH. 67 



albumen and sterilized by heat. This was carefully reduced 

 to a jelly that would solidify on cooling, and spread in a thin 

 layer on glass slides suitable for microscopic examination. 

 When the slides were thus prepared, a needle was dipped in 

 the fluid containing the organisms and drawn quickly across 

 the surface of the prepared culture medium, in such a way as 

 to distribute the few that adhered to the needle, along the 

 line of its track. This preparation was then sealed up, or 

 otherwise protected from contamination, and kept at a suitable 

 temperature for the growth of the organisms, and occasion- 

 ally examined with the microscope. It was found that the 

 organisms grew well on such soil or food ; also, that it re- 

 quired the utmost care to prevent contaminations. These, 

 however, could be detected by microscopic examination, and, 

 whenever found, rejected. It was also found that the differ- 

 ent organisms present in a fluid could be separated by this 

 method of culture; for in drawing the needle point along 

 the surface of the solidified jelly, the organisms would often 

 be distributed singly, and would develop in little groups that 

 could be seen by the naked eye. The characters of each could 

 be determined by the microscope. These were generally found 

 in the form of little flakes on the surface of the jelly, and 

 each could be detached with a needle and conveyed to another 

 slide, or when desired, to a culture fluid, and kept pure. 

 From these pure growths the organisms are transplanted to 

 other slides, or culture fluids, at will, and for any number of 

 generations, and kept absolutely pure. Inoculations were 

 made with these pure cultivations; and such inoculations 

 were found constant in their effects, whether taken from the 

 fifth or the one hundredth generation. 



By this process, it is believed that the difficulty heretofore 

 existing, as to the exclusion of a possible chemical ferment, 

 has been incontestably overcome. The phenomena are watched 



A* 



