68 Profs. H. Marshall Ward and. J. Reynolds Green. 



As it is not at present proposed to deal with the yeast, which ap- 

 pears to be a mere variety of S. cerevisice, we pass on to the cultures of 

 the bacterium only. 



On repeating the plate cultures exactly as before, except the exhaus- 

 tion and filling with carbon dioxide, it was found that mixtures of the 

 yeast and bacillus grew as well in air as in carbon dioxide. At first it 

 seemed possible that this was because the yeast rapidly consumed the 

 oxygen and so prepared an oxygen-free atmosphere for the bacterium, 

 but further experiments proved that this is not necessary, and that 

 both yeast and bacterium can be grown in air as well as in carbon 

 dioxide or in hydrogen. 



The appearance of the separated bacterium on the sugar-gelatine 

 plates is that of circular, raised, dome-shaped, watery-looking colonies, 

 stiff, like a firm jelly, and lifting as a whole on the needle. Each 

 colony is, in fact, a firm zooglcea composed of short rodlets in pairs or 

 chains, the cell-walls of which are so swollen as to furnish the zoogloea 

 jelly. The average size of these rodlets is 2 — 3 fi long by 1 p thick, 

 though much longer rods and filaments occur in other media. 



Having once obtained the organism in pure culture, it was, of 

 course, easy to test its behaviour on various media. It is unnecessary 

 to enumerate all the media tried, or to give details of the cultures, 

 which amount to several hundreds ; enough that all ordinary media 

 employed by bacteriologists were tried, as well as a long series of 

 special ones devised to meet the suggestions which arose during the 

 course of the investigation. 



A striking fact comes out on surveying these cultures, namely, this 

 Schizomycete practically refuses to grow in or on any pabulum devoid 

 of sugar, and, further, only certain sugars are capable of supplying it 

 with its necessary food. No growth at any temperature could be 

 obtained in normal gelatine-peptone media, or in broth, milk, or other 

 animal extracts, e.g., serum-agar, such as is used by the animal 

 pathologists. 



Gelatine Cultures. 



Gelatine, 10 per cent., added to "black sugar" solution* 15 per 

 cent, is a capital medium for cultures at 18° C, or thereabouts, and in 

 air, in hydrogen, or in carbon dioxide, the bacterium formed prominent 

 domed colonies looking like drops of stiff gum or gelatine. 



This black-sugar gelatine was also used for cultures in vacuo. Plates 

 kept under a receiver permanently attached to the pump, going day 

 and night continuously for a week, showed traces of colonies in eight 

 days, and in fourteen days the colonies in the exhausted receiver were 



* This " black sugar " is a very dark coarse Demerara sugar and probably contains 

 considerable quantities of mineral and other matter. 



