222 BACTERIOLOGY 



finds a somewhat different situation in every host attacked. The 

 problem of the immediate future is to determine where the brilliant 

 discoveries of Metchnikoff, Nuttall, Behring, Bordet, Ehrlich, and 

 others belong in the life of each microbe, and to construct for each 

 disease the exact nature of the contest. 



in the following pages I do not intend to enter into any discussion 

 concerning the intimate life of bacteria, but simply to point out cer- 

 tain biologic problems which seem to lie on the surface, as it were, 

 and which illustrate the close relation existing between bacteriology 

 and general biology. They have suggested themselves to me from the 

 comparative standpoint, one up to the present but poorly cultivated 

 in medical science. 



The researches of Roux, Kitasato,and Behring, Van Ermengen and 

 others, have shown that certain species of bacteria secrete toxins 

 during their vegetative period. These toxins are soluble in the me- 

 diums in which these species multiply. Besides these physiologically 

 well-defined poisons, there are others which are closely linked to the 

 body substance of the bacteria, and which have become familiar to 

 us in such well-known substances as tuberculin and mallein. According 

 to the theory of R. Pfeiffer, this second class of poisons is liberated 

 only by the disintegration of the bacteria, and the intoxication of 

 the host, due to its destructive action on the bacilli, is a kind of post- 

 mortem effect of the parasites. Other bodies, the so-called lysins, which 

 act destructively upon red and white corpuscles, have also been de- 

 monstrated by Van de Velde and by Ehrlich and his pupils, but their 

 significance in disease is not yet clear. 



In the host, on the other hand, during the multiplication of micro- 

 organisms, there appear bodies known as anti-bodies, which have 

 aroused the greatest interest. They neutralize the soluble toxins, 

 agglutinate the invading bacteria and disintegrate them. They also 

 precipitate or coagulate albuminous bodies. Their action is specific, 

 being directed toward the invaders. These are the main weapons 

 which thus far have been found. Are there other offensive and de- 

 fensive bodies? What course do the bacteria pursue in the presence 

 of the gradually accumulating anti-bodies of the host? Do they forge 

 new weapons or not? 



Professor W. H. Welch in his Huxley lecture presented the theory 

 that the mechanism of the production of anti-bodies on the part of the 

 invaded host was set in operation by the micro-organisms as well, and 

 that various tissue poisons might have their origin in overproduced 

 bacterial receptors thrown off under special stimulation by host 

 substances. This theory implies that bacteria may not unfold all their 

 activities in the culture-tube, and that the latter give us no reliable 

 clue as to their behavior in the living body. 



On this point we may perhaps get some light by a consideration of 



