56 Lectures on Bacteria. [ vi. 



stances, compounds of nitric acid or still better of ammonia. 

 In addition to these a small supply quantitatively and quali- 

 tatively is required, as in other plants, of soluble constituents of 

 the ash. 



It does not fall within the scope of these lectures to go more 

 deeply into the consideration of the value of the several com- 

 pounds as food-material; on this point the special literature, 

 especially Nageli's publications (27, 28), should be consulted. 

 It is sufficient for our general guidance and for practical pur- 

 poses to observe that according to Nageli's investigations a 

 number of moulds and Sprouting Fungi as well as Bacteria also 

 can find their food in solutions which contain nitrogenous and 

 non-nitrogenous nutrient substances in the following compounds 

 or combinations, the several solutions being arranged and 

 numbered in descending order according to their nutritiveness : 

 i. Proteid (peptone) and sugar. 2. Leucin and sugar. 3. 

 Ammonium tartrate or sal-ammoniac and sugar. 4. Proteid 

 (peptone). 5. Leucin. 6. Ammonium tartrate or ammonium 

 succinate, or asparagin. 7. Ammonium acetate. 



But we must not seek to determine or judge of the optimum 

 of feeding - quality for all species or forms of Bacteria from 

 this table. The above scale is not even true for all moulds, 

 though it was first drawn up from the study of one of that group, 

 Penicillium glaucum. The requirements in the way of food of 

 single definite species of Bacterium have as yet been little studied, 

 and much needs more exact investigation. A number of prac- 

 tical experiences, which will be partly noticed further on under 

 the particular examples, point already to the great multiplicity 

 of the actual relationships which have to be taken into account. 



Besides the amount of suitable food-material contained in the 

 substratum, other chemical qualities in it are also of importance 

 to the vegetative process in Bacteria. It is an old experience 

 that most of these organisms^ in contrast to the reverse be- 

 haviour of Sprouting Fungi and moulds, flourish best, other 

 conditions being the same, in a medium with a neutral or 



