H. B. Hutchinson and J. Clayton 147 



sodium nitrate and 1-5 per cent, agar; this stock agar was tubed in 

 portions of 10 c.c. and sterilised in the autoclave. A number of such 

 sterile portions were then poured into a like number of Petri dishes and, 

 after consolidation of the medium, a circular piece of sterile filter paper 

 was laid and pressed upon the surface of the agar. Fresh portions of the 

 melted agar were then inoculated with various dilutions of the culture 

 to be plated out and were then poured in as thin a layer as possible over 

 the surface of the paper. In this manner plates were obtained which 

 on incubation for upwards of a week showed quite strong bacterial 

 growth, the paper became covered with bright yellow spots (colonies), 

 and eventually became transparent owing to the complete dissolution 

 of the paper (Plate I, fig. 1). 



Although otherwise satisfactor}- growth of the causative organisms 

 could be obtained in this manner, this method of preparing plate 

 cultures was abandoned ; in the first place, because the colonies uniformly 

 gave what were regarded as impure growths, and, secondly, on account 

 of the fact that the colonies resulting from the inoculation of any one 

 plate appeared to bear little relation to the number of organisms actually 

 used as inoculant. 



The second method consisted in the preparation of a suspension of 

 cellulose by grinding up filter paper with coarse sand and water. By 

 this means a quantity of finely divided cellulose was obtained and made 

 into agar similar in composition to the preceding one. The preparation 

 of cultures with this medium gave, after upwards of 8-10 days, plates 

 showing a number of zones in which, by the growth of the organism, the 

 cellulose had become partially or wholly dissolved (Plate I, fig. 2). 

 Microscopical examination of plates from crude cultures revealed the 

 presence of numerous surface and embedded colonies which, however, 

 had no obvious connection with the zones of change, and which on 

 transference to filter papertubes did not result in characteristic breakdown 

 of the paper. Microscopical examination of the agar of the zones was 

 made and showed the presence of two chief cell forms which have also 

 been invariably found in cultures capable of inducing active and typical 

 decomposition. One of these forms, usually referred to as the "thread" 

 form, was found in abundance in young cultures on agar or on paper, 

 and consisted of a fairly long thin filamentous and frequently curved 

 cell, that was stained with difficulty by ordinary methods. The second 

 form was that of a large " coccus " which, particularly in old cultures, 

 occupied a predominant position. 



From time to time we were able to obtain colonies on cellulose agar 



10—2 



