104 METHODS OF PURE CULTURE 



test-tubes can be treated by moistening the cotton plug with formalin and then 

 covering it with a rubber cap to prevent desiccation. Plates and cultures in 

 Petri dishes can be kept for some time by covering them with filter-paper 

 moistened with the same antiseptic, which kills the cultures without destroying 

 their form. It also penetrates the medium, hardens the gelatin, and makes it 

 unsuitable for the further development of organisms, so that the preparations 

 thus treated are exceedingly durable. Fuller information on the preservation 

 of pure cultures of fermentative organisms, and practical hints concerning the 

 arrangement of mycological museums, which are very useful both for teaching 

 and for reference purposes, will be found in the treatises prepared by J. SOYKA 

 (I.), F. KRAL (I.), H. PLAUT (I.), E. CZAPLEWSKI (I.), and E. KRUCKMANN (I.). 



The necessity will not infrequently arise for reliable (living) pure cultures 

 of authoritatively named species of bacteria, &c., either for use as a starting- 

 point for sudy or for comparing, and, as far as possible, identifying some 

 newly-discovered species. Krai's Bacteriological Laboratory (n Kleiner Ring, 

 Prague I.) can be recommended as a source from whence to obtain them. This 

 institution supplies living pure cultures, streak-cultures on oblique solidified 

 agar-agar, in test-tubes at the moderate price of one to two marks ( = shillings) 

 per tube. 



Koch's plates can also be used with advantage when it is a question of 

 ascertaining which nutrient media are suitable for a given microbe. For this 

 purpose BEYERINCK (VIII.) has devised a method which he calls Auxanography. 

 A 10 per cent, gelatin or 2 per cent, agar-agar in distilled water is prepared, 

 both of which substances in the pure state form very bad media, whether for 

 bacteria or higher fungi. Plate cultures of the micro-organism whose nutritive 

 requirements form the object of the investigation are then prepared. These, if 

 left to themselves, will not exhibit any appreciable degree of development, so 

 the surface of the plates is stippled with a few drops of aqueous solutions of the 

 substances whose nutrient properties are to be tested. These drops are absorbed 

 by the gelatin or agar-agar, and form circular fields of diffusion around the 

 spots in question. The thickly sown cells of the species under examination will 

 then develop into strong colonies on those spots only where the requisite nutrient 

 materials are encountered, so that the organisms inscribe, as it were, with their 

 bodies, the answer to the question propounded as to the suitability of the 

 nutrient substances at hand. Such a plate of colonies grown in this manner is 

 called by Beyerinck an Auxanogram. This method may also be employed for 

 testing the toxic action of various substances on given organisms. BEYERINCK 

 (IX.) also employed this process as a basis for the qualitative and quantitative 

 method of microbiological analysis proposed by him in the reference just given. 



