820 



SCIENCE. 



[N. S. Vol. XX. No. 520. 



These toxins ai*e soluble in the mediums 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 mal- 

 lein. According to the theory of R. 

 Pfeiffer, this second class of poisons is lib- 

 erated 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 para- 

 sites. Other bodies, the so-called lysins, 

 which act destructively upon red and white 

 corpuscles, have also been demonstrated 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 microorganisms, there 

 appear bodies known as antibodies, 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 spe- 

 cific, being directed toward the invaders. 

 These are the main weapons which thus far 

 have been found. Are there other offens- 

 ive and defensive bodies? What course 

 do the bacteria pursue in the presence of 

 the gradually accumulating antibodies" of 

 the host? Do they forge new weapons or 

 not? 



Professor W. H. Welch in his Huxley 

 lecture presented the theory that the mech- 

 anism of the production of antibodies on 

 the part of the invaded host was set in 

 operation by the microorganisms as well, 

 and that various tissue poisons might have 

 their origin in overproduced bacterial re- 

 ceptors thrown off under special stimula- 

 tion by host substances. This theory im- 

 plies that bacteria may not unfold all their 

 activities in the culture tube and that the 



latter give iis no reliable clue as to their 

 behavior in the living body. 



On this point we may perhaps get some 

 light by a consideration of the plasticity 

 of microorganisms. It has long been known 

 that the pathogenic power of bacteria is 

 reduced gradually in artificial cultures. It 

 is also well known that by a series of inocu- 

 lations or passages through animals the vir- 

 ulence may be restored, and even raised 

 above the natural level. Bacteria have 

 been gradually accustomed to originally de- 

 structive doses of poisons in culture fluids. 

 Very recently it has been shown that they 

 may be gradually trained to multiply in 

 strongly bactericidal serums and to refuse 

 to be clumped in strongly agglutinating 

 serums. 



These adaptations persist for a certain 

 time and are transmitted for a limited pe- 

 riod, even in culture. In other words, the 

 modifications are more or less gradually 

 acquired and gradually lost. The same is 

 true of the antibodies of the host. The 

 antitoxin circulates in the blood of the 

 horse long after the stimulation by toxins 

 has ceased. In the immunized animal the 

 agglutinating properties do not disappear 

 at once. I am, therefore, inclined to be- 

 lieve that the bacterium freshly removed 

 from its usual environment will, at least 

 for a time, exercise all its functions, pro- 

 vided the special nutritive substances 

 which may be needed to carry on those 

 functions are present. 



The theory of Professor Welch would 

 then resolve itself into a question of nutri- 

 tion. In the body of the host there are 

 certain substances which give rise to special 

 toxins when acted upon by special bacteria. 

 If we could offer these special substances 

 to freshly isolated bacteria there is no rea- 

 son why the assumed toxin should not be 

 formed. We must, therefore, take into ac- ' 

 count two possibilities, the adaptation of 

 microbes to originally destructive agencies. 



