KOCH'S PLATE CULTURES. 133 



applicable to fungi alone, its application to other groups having 

 been successful in the case of a few only of the lowest unicellular 

 algae. In this manner BEYERINCK (VI.) prepared pure cultures of 

 the last-named organisms (frequently found in the microscopic 

 examination of river-water), viz., Chlorella vulgaris, Scenedesmus 

 acutus, Chlorosphcera limicola, Chlorococcum (Cystococcus) liumi- 

 cola, Stichococcus major, and a second species of Chlorella. WIL- 

 HELM KRUGER (I.) prepared by the plate method pure cultures of 

 two algae, which he named Chlorella protothecoides and Chlorothe- 

 cium saccharophilum, from the sap of the lesser maple. Quite 

 recently BEYERINCK (VII.), A. CELLI (I.), FR. SCHARDINGER (I.) and 

 others, have also successfully attempted the cultivation of Amoeba 

 an the same manner. 



The solid nutrient media in question are, except those contain- 

 ing chalk, transparent, so that the plates prepared therefrom can 

 be laid on the stage of the microscope and their colonies examined 

 under a low power by transmitted light. The differences thereby 

 observable form valuable indications for the identification of the 

 individual species. A number of them, Bacillus subtilis for ex- 

 ample, excrete a peptonising enzyme, in consequence of which the 

 gelatin is liquefied as far as the solvent enzyme proceeding from 

 the colonies is able to diffuse, and thus a liquefactive colony is 

 obtained. The converse was supplied by such organisms as pro- 

 duce no enzyme aapable of dissolving gelatin, and which therefore 

 do not liquefy the medium, but grow as solid colonies. The 

 development of these latter may proceed in various ways ; the 

 colonies of Bacterium aceti, for instance, gradually assuming a 

 stellar form, whilst those of the lactic acid bacteria have a circular 

 outline. Bacillus ramosus a fission fungus frequently occurring 

 in soil and in natural waters, and generally known as wurzel 

 (root) bacillus which M. WARD (IV.) subjected to exhaustive 

 morphological and physiological examination, grows on agar-agar 

 to colonies built up of entangled, branched, and plaited threads 

 resembling the roots of a tree. A comprehensive description of 

 these characteristics, as presented by the separate species of bac- 

 teria, will be found in Eisenberg's work. 



If a platinum wire, previously heated to redness and then 

 dipped in a bacterial culture, be thrust into a solid medium con- 

 tained in a test-tube, the cells so implanted in the passage formed 

 by the wire will develop to a so-called puncture culture, the 

 appearance of which also affords valuable indications for the re- 

 cognition of individual species. Organisms requiring air grow 

 only on the surface, whereas those shunning the air will develop 

 only in the deepest part of the channel, and those dissolving the 

 gelatin will form a liquefied funnel. This latter indication is one 

 developed in a highly characteristic manner by the cholera bacillus, 

 and is, therefore, made use of in the bacteriological analysis of 

 water. If a test-tube containing about 8 or 10 c.c. of liquefied. 



