316 DE NOVO OEIGIN OF BACTERIA 



are associated with the growth and multiplication of "living 

 speciiac organisms" a belief in the de novo origin of these con- 

 tagious diseases would "imply also a belief in spontaneous 

 generation." This latter notion is undoubtedly very common 

 and has been one of the principal causes that has stood in the 

 way of a belief in the possibility of the de novo origin of a contagious 

 disease. On this account, therefore, the proof of the heterogenetic 

 origin of Bacteria becomes a matter of very great importance for 

 medical science. Still, the conclusion above drawn, notwithstanding 

 its prevalence and great influence, does not of necessity follow, as 

 I shall hope to show. 



We all know that common Bacilli and Micrococci are constantly 

 making their entry into the body through the intestinal and the 

 respiratory mucous membranes, and thence are gaining access to 

 the lymphatic system. So that for the origin of this or that specific 

 disease it may not be at all necessary that a de novo origin of 

 microorganisms should take place. Under the influence of un- 

 healthy local or general conditions the common microorganisms thus 

 entering into the body may possibly be made to take on new 

 properties and be, in fact, converted into one or other of the so- 

 called " specific " or " pathogenic" microorganisms. 



It is needless for me to cite in support of this latter possibility 

 the vast array of facts now known concerning the variations and 

 interchangeability of form that may be brought about in these 

 microorganisms by changes in the media and conditions to which 

 they are subjected, and the still more important variations in 

 function and in the chemical processes associated with their 

 growth and multiplication that may be similarly induced. This 

 is so notoriously the case that many writers, such as Billroth, 

 Nageli, Warming, Cienkowski, Ray Lankester, Kopf, and others 

 have regarded these microorganisms as mere phases or varieties, 

 modified by external conditions, of one and the same, or of but a 

 very few distinct species. Many facts of importance in this relation, 

 in connection with pathogenic Bacteria and their possible deriva- 

 tion from non-pathogenic forms, are matters of common knowledge. 



There is one case, however, so pertinent to the present inquiry 

 and of such great importance in itself that some details will prove 

 most useful. I allude to our present knowledge concerning certain 

 experimentally produced diseases in lower animals included under 

 the name Septiccemia. Two of these forms of septicaemia have 



