COMBATING PARASITIC BACTERIA. 167 



have grown up so slowly as to be hardly appre- 

 ciated are really great triumphs. For instance, 

 the study of bacteriology first led us to suspect, 

 and then demonstrated, that tuberculosis is a 

 contagious disease, and from the time that this 

 was thus proved there has been a slow, but, it is 

 hoped, a sure decline in this disease. Bacterio- 

 logical study has shown that the source of chol- 

 era infection in cases of raging epidemics is, in 

 large part at least, our drinking water ; and since 

 this has been known, although cholera has twice 

 invaded Europe, and has been widely distributed, 

 it has not obtained any strong foothold or given 

 rise to any serious epidemic except in a few cases 

 where its ravages can be traced to recognised 

 carelessness. It is very significant to compare 

 the history of the cholera epidemics of the past 

 few years with those of earlier dates. In the epi- 

 demics of earlier years the cholera swept ruth- 

 lessly through communities without check. In 

 the last few years, although it has repeatedly 

 knocked at the doors of many European cities, it 

 has been commonly confined to isolated cases, 

 except in a few instances where these facts con- 

 cerning the relation to drinking water were ig- 

 nored. 



The study of preventive medicine is yet in its 

 infancy, but it has already accomplished much. 

 It has developed modern systems of sanitation, 

 has guided us in the building of hospitals, given 

 rules for the management of the sick-room which 

 largely prevent contagion from patient to nurse; 

 it has told us what diseases are contagious, and in 

 what way ; it has told us what sources of conta- 

 gion should be suspected and guarded against, 

 and has thus done very much to prevent the 



