2 6 TEXTBOOK OF BOTANY 



as they are called, as well as persons who are suffering from 

 a light attack which is not recognized as typhoid, are a soiarce 

 of danger to others, especially if they are careless or un- 

 cleanly in their habits. One case of a typhoid carrier that 

 has been carefully studied was that of a cook ; in several 

 families in which she worked for a term of years typhoid cases 

 occurred, and she was the cause of a number of deaths. An 

 outbreak of typhoid fever involving forty-one cases and three 

 deaths occurred at Madison, Wisconsin, in the fall of 1908, 

 among those who lived or ate at a certain boarding house. 

 The source was found to be a student who was employed in 

 cleaning and wiping dishes and who had returned to Madison 

 in the fall in the early stages of typhoid fever. Sufferers 

 from typhoid are not immune to the disease after recovering 

 from it ; they may be repeatedly attacked. However, an 

 artificial immunity can be produced by vaccination with 

 typhoid bacilli that have been killed by heat or other means ; 

 and the use of this method of vaccination has practically 

 eliminated typhoid from the armies of many nations. 



39. Lockjaw. — The germ of lockjaw or tetanus (Fig. 9, 

 I?), is a bacillus that lives in the soil and is found practically 

 everywhere. The disease, like diphtheria, is caused by a 

 toxin which is given off by the bacillus and is taken up by the 

 blood. Infection occurs from soil that gets into cuts and 

 wounds. It follows that a cut should always be thoroughly 

 cleaned and then treated with an antiseptic, such as iodine, 

 which will check the growth and reproduction of any bacteria 

 that may be present. We have already seen that the wound 

 should not be so tightly covered as to prevent the entrance 

 of air, because it is in the absence of air that the tetanus 

 bacillus thrives. 



40. Anthrax. — This is a serious disease of cattle and 

 sheep. It is highly contagious and difficult to combat, 

 partly because the spores of the anthrax bacillus are very 

 resistant to drying and can live in the soil for many years. 



