DISEASES THAT SPREAD 



313 



In the preceding chapters we have learned a few of the 

 simplest principles which underlie the maintenance of good 

 'health. 



We are now to study very briefly other means which 

 are used to prevent and restrict the spread of disease. 

 One of the most common safeguards against the spread 

 of disease is the use of 

 vaccination as a protection 

 against smallpox (Sec. 

 256). That is, persons 

 who are vaccinated are 

 " immune," as it is called, 

 from smallpox, or have it 

 in a milder form. 1 



Another very common 

 safeguard against the 

 spread of contagious dis- 

 eases is isolation. The 

 patients, and often the 

 family, are isolated from 

 other people; a rigid 

 system of nursing is in- 

 stituted ; a placard is placed upon the house ; the premises 

 are watched; and other familiar means of isolation are 

 employed. 



1 Since the use of animal vaccine has taken the place of the old-time 

 arm-to-arm vaccination, there is little or no danger of inoculating any kind 

 of disease with the vaccine. The use of unclean tools, undue exposure to 

 inclement weather, and neglect or improper treatment of the vaccination 

 wound are often the cause of much unnecessary suffering. As the pro- 

 tective power .of vaccination gradually becomes weak with time, it is wise 

 to repeat it every ten years at least. Any one exposed to smallpox ought 

 always to be revaccinated, no matter how recently the operation may have 

 been performed. 



FIG. 199. Rod-Shaped Bacteria, or 

 Bacilli, which cause Lockjaw. 



Magnified about 1000 times. 



