106 APPLIED BACTERIOLOGY 



taken to prevent spread of disease may be divided into two 

 classes : 



1. (a) Vaccination ; (b) Quarantine ; (c) Notification and 

 isolation. 



2. Disinfection of the person, clothes, home, and dis- 

 charges of the patient. 



It would be obviously out of place to deal with general 

 preventive measures here, but the considerations involved 

 in practical disinfection may fairly be included, and will be 

 considered in detail. 



By far the greater number of pathogenic organisms given 

 off ultimately from any case are destroyed by what we may 

 term ' natural disinfection '; for example, by the action 

 of light and air, or by meeting with conditions of soil and 

 temperature unfavourable to their growth ; or, again, they 

 may be crowded out by saprophytic bacteria that are more 

 capable of life under the existing conditions. Again, a 

 certain number of organisms, varying in different cases, are 

 required to produce a toxic dose — that is to say, to make 

 headway as invaders against the healthy tissues; the 

 number of organisms thus required doubtless varies with 

 the age and condition of the subject, the state of the 

 tissues, and the condition of virulence or attenuation of 

 the organism, while hereditary tendencies and other in- 

 fluences must not be neglected. 



It is in many cases advisable to attend to careful disinfec- 

 tion of the body of the patient — for example, in the case of 

 small-pox, measles, scarlet fever — while after diphtheria the 

 throat should be disinfected by means of a suitable gargle 

 till the Klebs-Loffler bacillus can no longer be found on 

 inoculation of serum-tubes. For disinfecting the skin or 

 the hands previous to an operation, a solution of mercuric 

 chloride (1 in 1,000) is convenient, the skin having been 

 well cleaned with soap and water, ether, turpentine, or 

 other suitable grease solvent. 



