BY R. GREIG-SMITH. 155 



A rod-sliaped bacillus, Bac. A17, which had appeared to 

 stimulate the growth of Bac. prodigiosus in collodion-capsules, 

 was tested in hay-infusion, but there was no evidence of toxin 

 formation in the boiled or diluted extracts. 



In view of the indeterminate nature of the results hitherto 

 obtained, it was deemed advisable to augment the intensity of 

 the growth of the bacteria by increasing the amounts of the 

 nutrients and by aerating the media during cultivation. To gain 

 this end, beakers containing cotton-wool were sterilised, and 

 media, such as 1% hay-infusion with and without 1% dextrose, 

 which had been seeded with various organisms, were added in 

 sufficient quantity to moisten the wool. After incubation at 

 22°, the cotton-wool was squeezed and washed, and the liquids 

 made up to a definite volume before being filtered through 

 porcelain. 



A soil-Rhizobium, Bac. T.P.2, Penicillium cladosporioides, and 

 an Actinomyces, A 10, were tested at difierent times, such as 3, 

 6, and 11 days; but, in none of the tests, was any evidence of 

 toxin-formation demonstrated. This also applied to old cultures 

 of bacteria reinfected with moulds. The method was useless, 

 therefore, for the object in view. 



The experiments, however, raised the idea that small changes 

 in the reaction might be responsible for much of the irregularity 

 in the results. Bacterial cultures, in the absence of a ferment- 

 able sugar, are generally more or less alkaline, while soil-extracts 

 are supposed to be more or less acid. The soils used in this set 

 of researches were acid, that is to say, when a piece of litmus- 

 paper was inserted or pressed into a paste or porridge made by 

 mixing the soil with water, it became reddened in the course of 

 a few minutes. The aqueous extract of such soils should, there- 

 fore, be acid, and it appeared that, if the extract could be pre- 

 vented from becoming alkaline through the action of bacteria, 

 there would be a better chance of demonstrating any development 

 of toxicity. At any rate, the cultural fluids would be more in 

 harmony with the conditions that pertain in the soil. To efiect 

 this faint, permanent acidity, it would be necessary to add some 

 substance which would absorb any alkalinity produced, in the 



