December 31^ 1915] 



SCIENCE 



929 



security. Sanitary regulations often in- 

 terfere with family management, the 

 schooling of children, the transportation 

 and selling of perishable goods, the estab- 

 lished practises of mining and manufac- 

 turing corporations and of small trades- 

 men, and even the personal habits of the 

 private citizen. These interferences are 

 sometimes abrupt and arbitrary. On the 

 whole, however, tlus teaching has been 

 wholesome in the freedom-loving nations, 

 in which individualism is apt to be exag- 

 gerated, and the sense of neighborliness 

 and social unity needs to be quickened. 



The rapid development of public sanita- 

 tion has also given important lessons on 

 promptly utilizing so much as we know of 

 applied science, but also modifying our 

 practises rapidly whenever the subsidiary 

 sciences effect an advance. Forty years 

 ago the filth and fomites theory was the 

 basis of sanitary practise. Municipal and 

 household cleanliness are still inculcated, 

 but the emphasis on them is no longer ex- 

 clusive. Then, bacteria and other disease- 

 producing organisms became the chief ob- 

 jects of interest for sanitarians, and sani- 

 tary practise was based on knowledge of 

 these organisms, and study of the media 

 through which they reached man, such as 

 the air, water, the soil, dust, milk and 

 other uncooked foods. Isolation of all 

 cases of contagious disease was much in- 

 sisted on. Isolation is still useful in many 

 cases; but it is not regarded to-day as the 

 one effectual defense against epidemics and 

 the diffusion of disease. Next, insect and 

 vermin carriers were made known, and 

 with them came in quite a new set of sani- 

 tary practises — not a replacement but a 

 lajge addition. Lastly, the contact theory 

 of contagion, with its demonstrations that 

 living bacteria may be carried from one 

 person to another in minute vesicles or 

 droplets thrown off in coughing, sneezing, 



or any convulsive effort, and borne on the 

 air, has gained general acceptance. At 

 the same time, abundant proof has been 

 given that pathogenic bacteria and protozoa 

 develop in the bodies of many persons 

 without causing any recognizable symp- 

 toms. Yet the virulence of the germs these 

 persons carry may be extreme. These re- 

 cent discoveries have introduced serious 

 difficulties into some departments of sani- 

 tary practise. The apparently healthy 

 carrier can not be isolated; for he remains 

 unknown. If at any time such carriers 

 and missed eases are numerous in a given 

 community, isolation becomes useless, if 

 not impossible. That is the ordinary con- 

 dition of most American communities in 

 regard to tuberculosis. Hence, bacteriol- 

 ogists have before them a very useful piece 

 of work in the study of human carriers of 

 disease who are not sick. Meantime sani- 

 tary practise is obtaining sound explana- 

 tions of the occasional failure of its former 

 methods of resisting epidemics, and pre- 

 venting the spread of the ordinary con- 

 tagious diseases. 



The principal lesson to be drawn from 

 the experiences of sanitarians during the 

 past fifty years is that practitioners of any 

 useful art must be prompt at every stage 

 of progress to make use of knowledge just 

 attained, even if it be empirical and incom- 

 plete, and must not linger content or satis- 

 fied at any stage. This lesson is applicable 

 in every modern industry and educational 

 or governmental agency during either 

 peace or war. 



Biologists are now realizing that bio- 

 chemistry must furnish the fundamental 

 knowledge of the processes which inces- 

 santly go on in the healthy body, and must 

 also provide the exact knowledge of those 

 changes in the normal processes which lead 

 to disease and death. The physician and 

 the sanitarian have become accustomed to 



