MICROSCOPICAL AND PHYSIOLOGICAL EXAMINATION. 31 



dividing the glass-cover into small squares or by means of the 

 object marker, and the apparatus is placed in the incubator 

 until the colonies are completely grown. On one cover-glass 

 there may be 50 to 60 well-isolated germs. When the colonies 

 are completely developed, they are transferred to flasks by 

 means of a small piece of platinum wire, which has been pre- 

 viously ignited and cooled. During this transference the 

 culture is for an instant in the air, and is here exposed 

 to contamination. But the danger of contamination at 

 this, the single weak point, is reduced to an insignificant 

 minimum, and disappears if the above-mentioned opera- 

 tion, be performed in a small enclosed germ-free space ; 

 as, for instance, in a small chamber with glass sides 

 which is sufficiently large to admit the apparatus and the 

 hands of the experimenter (see p. 14). In this way the 

 transference of the colonies is effected with all possible 

 security. From the first flask the culture can be transferred 

 without contamination to a continually increasing number of 

 larger flasks. Thus, Hansen's method approaches the desired 

 end as nearly as is possible, and is consequently employed 

 everywhere in exact experiments of this kind. 



As early as the year 1883 Koch's method of plate-culture 

 was tested by Hansen. He prepared a mixture of two species 

 of yeast which can be distinguished from each other micro- 

 scopically, namely, Saccharomyces apiculatus and a species 

 of the group Sacch. cerevisise. This mixture was introduced 

 into wort-gelatine, and after shaking was poured on to a glass- 

 plate. Of the specks formed, about one half contained one 

 species exclusively, the other half the other species, and in 

 one of the specks both species were found. 



Later (1888) a similar control was carried out for the 

 bacteria by Miq^lel, who introduced 100 colonies from a 

 plate-culture obtained in an air-analysis into 100 flasks 

 containing meai>broth with peptone. The examination of 

 the growths developed in the flasks showed that they con- 

 tained 134 different species of micro-organisms. The cause 



