METHODS OF INVESTIGATING BACTERIA. 803 



were present in relatively large numbers in the material 

 employed, and in many cases, even where we have to do 

 with pathogenic organisms, this condition is prohably 

 fulfilled; where, however, saprophytes of various kinds 

 are present in great excess, it is hardly feasible to hope 

 for complete separation by this method. 



In some cases it is well to combine the plate method 

 and the dilution method in order to obtain good results. 



The whole method of pure cultivation must of course 

 be practised in the first instance with some typical ex- 

 amples. As good specimens for this purpose I would 

 recommend the cultivation of bacillus prodigiosus on 

 potatoes, gelatine, &c., at various temperatures; the 

 cultivation of anthrax bacilli on potatoes, nutrient jelly, 

 blood serum, and in fluid substrata, likewise at various 

 temperatures ; the cultivation of Aspergillus flavescens 

 on slices of potato at a low temperature (15 to 20 C., 

 &c.). If every one who attempts the cultivation of 

 fungi, and especially the isolation of pathogenic organ- 

 isms, would first test their knowledge with these typical 

 examples, a great many imperfect papers would remain 

 unpublished. 



Having succeeded in obtaining a pure cultivation of A further 



A . . , differcntia- 



an organism, we have next to determine its morplio- tion of the 

 logical and biological characters. We have to ascertain 

 what are the nutrient materials, and what the tempera- 

 ture which most favour its growth, and whether, and in 

 what degree, it requires the presence of oxygen ; we have 

 to test whether it is able to excite fermentation, and for 

 this purpose we have to add the most important of the 

 fermentescible substances (carbo-hydrates, the higher 

 alcohols, fatty acids, albuminous materials, &c.) to the 

 ordinary nutrient materials, and under the other 

 conditions necessary for the growth of the organisms. 

 We have further to ascertain whether the organism 

 isolated has any pathogenic action ; inoculation experi- 

 ments must be made on a variety of animals, more 

 especially on mice, which are so very susceptible 

 to infective diseases, and also on guinea-pigs, rabbits, 

 monkeys, &c. These experiments must be carried out 



