VI PREFACE. 



Our knowledge of micro-organisms is as yet so imperfect that 

 for the present we absolutely require some such rough method of 

 making ourselves mutually intelligible. The attempts to classify 

 bacteria according to other principles, and with reference to their 

 ontogenetic and phylogenetic development are doubtless justified, 

 but in view of the small number of definite observations are 

 premature, and at any rate for practical purposes are in the mean- 

 time completely useless. 



Xor can we form a practical classification on the basis of spore 

 formation, because in the case of most species it is very difficult 

 to decide whether, under what conditions, and how they fructify. 



On the other hand, by careful attention to the characteristics 

 of growth on certain soils, it is comparatively easy, as the 

 experience of several years has taught us, for the beginner to 

 find his way in the labyrinth of the forms of bacteria, and we are 

 certainly justified in the meantime in joyfully trusting ourselves 

 to this Ariadne thread, always bearing in mind that the indica- 

 tions so obtained are provisional and only pave the way for more 

 thorough knowledge. 



For the diagnostic summary attempted here it was necessary 

 to give names as far as possible to the individual species of 

 bacteria. The culture characteristics have for the most part 

 formed the bases for these names, and hence they have, like the 

 classification itself, only a provisional importance, and are only 

 justified in so far as they render mutual understanding easier for 

 the present. Should some authors be dissatisfied with the names 

 which have here been chosen for the bacteria first described by 

 them, they may excuse my action when they remember the 

 necessity for a terminology, the provisional character of the 

 names, and the possibility of altering them at any time. 



Some of the more common forms of saprophytes collected in 

 this Hygienic Institute are only described incompletely, and with 

 almost exclusive reference to the characters which are of use in 

 differentiating them. A more complete study of these forms is 

 proposed at a later time. I am deeply indebted to the workers 

 at the Institute, Drs. Oberdiek, Henrijean, Guarncri, Kreibohm, 



