BY R. GREIG-SMITH. 283 



the yield. There are, of course, traces of saline matter in the 

 agar and tap-water which may be sufficient to nourish the 

 bacterium. A small quantity of salt is, however, in some cases 

 preferable, and in all cases the addition of say 0'2 % of a salt will 

 not diminish the slime to any considerable extent. 



One generally looks upon - 5 % as being the usual amount of 

 s<alt that should be in the great majority of bacteriological media, 

 chiefly because it is employed in the cultivation of bacteria 

 pathogenic to animals. There is no reason why that percentage 

 should be employed in growing all bacteria. It is only from 

 experiments such as this, in which the influence of the s-alt can be 

 definitely determined by the weight of the product, that the 

 optimum quantity of salt can be really ascertained. 



We have seen that for the production of slime, the optimum 

 quantity of nitrogen lay between O01 1 % and 0-015 %, equivalent 

 to 06 % and 08 % of asparagin, and also that the most suitable 

 amount of salt lay between zero and 0-2%. It is interesting to 

 note that this is not far removed from the amount of these con- 

 stituents in soil water. With regard to the nitrogen, the nearest 

 approach that we can get to the composition of actual soil water 

 is found in the analyses of drainage waters which consist of soil 

 water diluted with rain, and in these the nitrogen varies from 

 0-0015% to 0-005%. According to Nobbe and others, plants 

 grow in fluids containing from 005 % to 0-2 % of saline matter, 

 the growth being most luxuriant with - l %. This is slightly 

 stronger than the drainage water of fields which contains about 

 0-05% of dissolved mineral and organic matter. These percentages 

 are, however, so close to that experimentally found for the optimum 

 slime-production, that it may be accepted that so far as nitrogen 

 and saline matter are concerned, the water of the soil maintains 

 the slime-forming faculty of this bacterium in an active condition 



Since the saline and nitrogenous matters of the soil suffice for 

 the wants of the micro-organism, the carbohydrates of the root 

 sap must be the substances that induce it to enter the root hairs. 



