122 TEXT-BOOK OF BACTERIOLOGY. 



stances which we have no right to suppose belong, all of them, 

 to the bases or ptomaines like those investigated by Brieger to 

 chemical examinations; and, on the other hand, the fact that the 

 different bacteria do not, as a rule, form only one definite substance, 

 but always produce several, which by their common joint effects 

 produce the pathological complex of symptoms which we regard 

 the micro-organism in question as answerable for. But the greater 

 the number of these competing poisonous substances, the more 

 difficult is it to separate them and test their several qualities. 



Although our present knowledge of this subject may still be 

 very deficient, and though it may call loudly for completion, yet 

 from what we do know we may safely lay down the proposition : 

 the action of the pathogenic bacteria is chiefly to be explained by 

 their producing specific, extremely poisonous substances which 

 seriously injure the organism, influencing it in a definite manner 

 and thereby causing definite independent forms of diseases. 



Just as the small portion of poison injected by the sting of a 

 bee or the tooth of a serpent suffices to cause local derangements 

 of considerable extent, to cause disturbance in the whole organ- 

 ism or even to kill it, so also the bacteria, by means of their toxine, 

 are under some circumstances able to affect parts with which they 

 come into no direct communication. In this way we must explain 

 the cases in which a general derangement of the bodily functions 

 reveals a violent disease, and yet the most careful search only finds 

 a very limited number of micro-organisms, or only finds them lim- 

 ited to one particular portion of the body, which for some reason 

 or other they adhere to exclusively. In the latter case they have 

 excreted their poison in their chosen quarters, it has been carried 

 far and wide by the blood and other juices, and its noxious effects 

 are seen wherever it has penetrated. 



If it is in reality the excretions of the bacteria which are the 

 great factors in their pathogenic agency, it will readily be compre- 

 hended that this agency cannot be fixed and definite in its amount, 

 but must be subject to considerable variations. 



The mere quantity of poisonous substance which, in different 

 cases, comes into the system must be taken into account. If the 

 disease-producing dose is attained or surpassed, pathological 

 changes present themselves which would otherwise have had no 

 existence. 



The nature and composition of the food on which the bacteria 

 are nourished and out of which their excretions are formed also 

 exercises an unmistakable influence. 



Here poisonous substances are composed or decomposed, while 



