Decembek 16, 1904.] 



SCIENCE. 



821 



and the production of poisons from specific 

 substances elaborated by the host. 



I have entered into this much of detail 

 concerning- the mutual relation of micro- 

 organisms and host in order to make clear 

 the hypothesis, which it seems to me ac- 

 counts very well for the general phenome- 

 non of infection. It is that the tendency of 

 all invading microorganisms in their evolu- 

 tion toward a more highly parasitic state 

 is to act solely on the defensive while secur- 

 ing opportunity for multiplication and es- 

 cape to another host. By tendency I mean 

 a general slow movement through long pe- 

 riods of time. The following data are in 

 its favor: 



1. The production of diffusible toxins 

 survives parasitism indefinitely, and is 

 readily brought about in cultures. 



2. Where toxin-producing bacteria have 

 become adapted to a definite species, as in 

 diphtheria, the toxin itself acts upon a 

 number of difi^erent species. In other 

 words, the parasitic relation is far more 

 specialized than the chief pathogenic 

 product. 



3. No strictly invasive bacteria have yet 

 been found producing diffusible toxins 

 which appear to be of any real significance 

 in the disease process. 



4. Those which produce such toxins are 

 not strictly invasive bacteria. 



5. The injury due to invasive bacteria is 

 known to be due to the disintegration of 

 bacteria and the setting free of poisons 

 locked up in the bodies of the microbes. 



6. Pathogenic bacteria manifest less bio- 

 cliemie activity than the related sapro- 

 phytic forms. 



7. The hemolytic and leukocidic toxins 

 of bacterial filtrates may be due to au- 

 tolysis of the bacteria. Jordan has shown 

 that hemolysis is at least in part due to a 

 change in the reaction of the culture fluid. 



According to this hypothesis, microor- 

 ganisms in slowly adapting themselves to 



the parasitic habit would gradually elim- 

 inate active toxin production and other 

 aggressive weapons as of little use, and 

 strengthen whatever defensive mechanisms 

 they may accidentally possess the rudi- 

 ments of. If these are capable of marked 

 development, we may expect such types 

 of disease as tuberculosis, leprosy, glanders 

 and syphilis, in which the parasitic habit 

 is carried to a high state of perfection. 

 If their mechanisms of defense are not 

 capable of much development they will 

 soon be destroyed or else become adapted 

 to live upon the skin, and especially the 

 mucous membrane as opportunists and oc- 

 casional disease producers. 



In this adaptation the possession of so- 

 matic poisons set free during disintegra- 

 tion may play an important part. They 

 may give rise to just sufficient toxin to 

 produce a local protecting nidus of ne- 

 crotic tissue, until the time for escape to 

 some other host arrives. This assump- 

 tion is supported by the fact that diseases 

 of some duration are usually focal in char- 

 acter. The microorganisms multiply only 

 in certain foci which sooner or later become 

 evident as the visible seat of disease. 



It may be claimed that defensive and 

 offensive methods are practically the same, 

 and that it is simply a play upon words to 

 make any distinction between them. But 

 reflectiorL will convince us that offensive 

 methods mean direct injury, whereas de- 

 fensive methods simply mean a neutraliza- 

 tion of the offensive weapons or else a 

 condition which is invulnerable to them, 

 such as an envelope made of a special sub- 

 stance. 



According to Ehrlich and his pupils, 

 the antibodies which appear in the course 

 of disease are not new bodies, but overpro- 

 ductions of bodies present in minute quan- 

 tities normally. The parasitic microbe is 

 thus at the very beginning of the invasion 

 confronted with these bodies. At the 



