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If foreign organisms capable of growing in the liquid 

 obtain, by any error of manipulation or other means, 

 access to the droplet, they may become in a few hours 

 diffused throughout its extent; if perceptibly different in 

 size or shape from the variety sown, the intrusion may 

 be detected and the culture abandoned ; if morphologi- 

 cally indistinguishable, the intrusion cannot be detected, 

 the culture is considered pure, and lamentable errors of 

 interpretation may result. Even in Koch's skilful hands 

 nearly one-half such cultures were found to contain foreign 

 organisms. 



Such, then, were the methods of attempted isolation in 

 general use until three years ago, and unfortunately still 

 extensively employed ; methods which, even in skilful 

 hands gave conflicting results, and in inexperienced hands 

 have demonstrated incredible things. By these methods 

 spontaneous generation is easily proven ; the metamor- 

 phosis of a pathogenic into an innocent bacterium, and 

 conversely, is established with great facility ; in fact 

 almost any plausible hypothesis can, with a reasonable 

 amount of ingenuity and inexperience, be clearly demon- 

 strated. It is difficult to conceive, indeed, a shorter road 

 to scientific notoriety than by the cultivation of bacteria 

 in flasks an opportunity already amply improved. One 

 need only extend his series of successive cultures long 

 enough, make transfers and pipette examinations often 

 enough, permit the temperature of his oven to vary a 

 little, perhaps spice his work with a touch of the fashion- 

 able evolution hypothesis by varying the composition of 

 his culture-fluids so as to invite the growth of various or- 

 ganisms, and, presto ! there appears a conclusion whose 

 adoption would revolutionize mycology, medicine, and 

 perhaps modern society. A bacillus may be made to 

 grow out of a bacterium, this out of a micrococcus, or any 

 of them out of nothing. A bacillus anthracis can, in the 

 course of fifteen hundred transfers, be robbed of its terrors 

 the leopard can change its spots, the lion can become 

 a lamb. 



Three years ago there was introduced thanks to the 



