January 24, 1908] 



SCIENCE 



133 



can be reinfected with new and more 

 virulent grafts with difficulty or not at all ; 

 and recently the interesting fact has been 

 discovered in Ehrlich's laboratory that in 

 such partially immune mice a tumor which 

 was originally adeno-earcinoma tends to 

 revert to adenoma, or from a more hetero- 

 geneous to a more homogeneous structure. 

 AVe see in this observation how funda- 

 mentally the state of the host reacts upon 

 the nature of the tumor, just as in the case 

 of increased virulence we saw how greatly 

 the state of the tumor cells reacted on the 

 host. And we can see the operation of 

 this reciprocal interaction of tumor and 

 host in the fundamentally important trans- 

 formations in types of tumor, from cancer 

 to sarcoma as shown by Ehrlich and Leo 

 Loeb, and from sarcoma to adeno-carci- 

 noma as observed by Jobling and myself, 

 which are part of the recent gains accru- 

 ing from the experimental study of tumors. 

 Then I might add a word on the outlook 

 for a more eiScient therapeutics of tumors, 

 now that tests can be made upon animals 

 under conditions of scientific accuracy of 

 experiment which will permit of the results 

 being interpreted in a strict rather than in 

 an empirical manner. Just as long as 

 every therapeutic advance had to be made 

 upon and with human beings the victims of 

 tumors, just so long was it impossible to 

 approach the subject in a truly scientific 

 way, for just so long was it impossible to 

 secure that control of experimental condi- 

 tions that alone can make biological ex- 

 periment accurate and advance logical and 

 not a thing of chance. 



I Avill now ask you to turn with me to a 

 brief discussion of certain topics in bacte- 

 riology which are compelling attention at 

 present. Bacteriology in relation to medi- 

 cine suffered from a period of reaction to 

 its many brilliant achievements and had 

 for a time lingered somewhat in' too famil- 

 iar fields. But new problems, the direct 



outgrowth of the old acquisitions, are open- 

 ing up and new lines of work are being 

 laid down, some of which are of such 

 gigantic importance to the larger interests 

 of social hygiene, that many new forces are 

 being brought into operation. 



Perhaps the chief single compelling phe- 

 nomenon is that of the microbe-carrier, 

 who is everywhere coming to be regarded 

 as a serious menace to the health of com- 

 munities. He is not a new discovery, for, 

 as regards diphtheria, he has been known 

 for more than a decade. But now he has 

 been found to disseminate tjrphoid fever, 

 dysentery, plague, cholera, influenza, spinal 

 meningitis, and in certain localities a host 

 of protozoan diseases. Moreover, he is not, 

 like the victim of tuberculosis, who is also 

 a microbe-carrier, a sufferer from the dis- 

 ease which he disseminates ; he is, as a rule, 

 immune to the microbes in an actual sense 

 and is usually ignorant of the sinister role 

 which he plays in life. The period of time 

 during which these pathogenic microbes 

 can exist in the body is very variable, but 

 may be great. In the case of typhoid fever 

 forty-two years have been known to have 

 elapsed since the attack, at the end of 

 which time typhoid bacilli were still being 

 eliminated with the dejecta. Plague bacilli 

 have been present in the sputum seventy- 

 six days after recovery from plague- 

 pneumonia; influenza bacilli have been 

 found in the sputum one year after an at- 

 tack of influenza; and still other examples 

 of long persistence of pathogenic microbes 

 could be cited. 



What is remarkable is that this persist- 

 ence of pathogenic germs in the body can 

 not be explained on the supposition that 

 they are really outside the body, residing 

 on mucous membranes, and hence not sub- 

 ject to the ordinary forces of destruction 

 which operate in the blood and tissues. 

 The typhoid bacillus increases chiefly in 

 the gall bladder, which is indeed not within 



