TEXT-BOOK OF BACTERIOLOGY. 131 



micro-organisms consume and which they also take from the living 

 tissues. 



Of far greater moment than the mechanical action and the con- 

 sumption of alimentary matter is another factor almost always at 

 work in the case of pathogenic bacteria. 



The micro-organisms excrete, as mentioned, certain substances 

 of peculiar composition. In most fermentations definite, specific 

 products arise. Thus in the decomposition of albuminous matter, 

 which, indeed, is entirely caused by the action of bacteria, particu- 

 lar substances are formed, a more exact knowledge of which we 

 owe specially to the important researches of Brieger. He ascer- 

 tamed very exactly the chemical constitution of a number of those 

 substances in which we see clear and tangible traces of bacterial 

 life, and found them to be bases— alkaloids— belonging principally 

 to the fatty compounds. 



Some of these substances, which from their origin have been 

 called by the general name of ptomaines (corpse-alkaloids), possess 

 extremely poisonous qualities, so that even small quantities of these 

 toxines' sufficed to kill the larger animals in a very short time. 

 But Brieger did not rest satisfied with these first results ; he soon 

 extended them very largely. The processes which lead to putre- 

 faction can only be observed with precision to a certain extent, 

 since they owe their origin to a great number of different and un- 

 known species of bacteria. It could not but seem desirable, there- 

 fore, to examine, in one and the same manner, certain micro- 

 organisms in pure cultures, and particularly to investigate the 

 excretions of the principal pathogenic species. And Brieger did, in 

 fact, succeed in making important discoveries by this method. He 

 found, for instance, that the cholera bacteria, the typhus and 

 tetanus bacilli, under suitable circumstances excrete specific sub- 

 stances out of their aliment — which prove to be genuine toxines, 

 and are able, when inoculated into animals, to produce some of 

 those phenomena which would be caused by the bacteria them- 

 selves. 



The importance of the excretions in the pathogenic agency of 

 micro-organisms was thereby placed beyond doubt, and efforts were 

 now made to discover a similar agency on the part of other species 

 besides those already mentioned. 



With some — for instance, with the anthrax and the diphtheria 

 bacillus, the vibrio Metschnikoff, etc. — a certain degree of success 

 has been achieved, though \vithout attaining that full degree of 

 certainty which distinguishes Brieger's investigations. The reason 

 is, on the one hand, the difficulty found in submitting these sub- 



