INTRODUCTION. 7 



excess and frequently at the expense of, some of the others, 

 sometimes even at the expense of the hving or resisting power 

 itself of the organism. In all cases, however, it should be 

 remembered that the differences in protoplasm are diiferences 

 in degree rather than in kind, and that the laws which govern 

 animal and other vegetable protoplasm govern the proto- 

 plasm of bacteria, and that the results of all investigations 

 that have been carried on in connection with them must 

 conform as strictly to physiological laws as any work that has 

 hitherto been done in the domain of animal or vegetable 

 biology ; and that where discrepancies of any kind, or appa- 

 rent departures from ordinary physiological laws, are met 

 with, the facts must be carefully revised, and if the dis- 

 crepancies still continue, then so much the worse for either 

 the facts or the laws. The " facts " are still incorrect or the 

 laws must be revised. 



There has grown, then, and still continues to grow, a 

 science dealing with microbiology in all its morphological 

 and physiological phases. Facts have gradually been accu- 

 mulated, observations have succeeded observations, patient 

 work and powerful concentration have played their part in 

 elaborating our knowledge of the habits of micro-organisms 

 without and within the higher plants and animals ; the 

 conditions under which the modes of life of micro-organisms 

 may be altered have been investigated ; the effects that 

 they or their secretions exert on living and dead proto- 

 plasm have been most conscientiously examined ; the 

 conditions that are essential in order that these organisms 

 may stimulate the activity of living protoplasm, and the 

 phases through which this protoplasm passes, from the 

 stimulated condition to degeneration and death, have all been 

 carefully studied. The organisms that have been found in 

 certain diseases have been identified and classified, their 

 modes of propagation and the channels by which they are 

 conveyed from one host to another, sometimes through 

 intermediate saprophytic or non-parasitic stages, have been 

 determined, and the whole subject has been so prepared, 

 that the great epoch-making minds of such men as Pasteur, 

 Chauveau, Lister, and Koch, being brought to bear on 

 these questions have found sufficient material at their 

 disposal on which to generalize, and have placed before the 

 world theories that appear to be more like fairy tales 



