farmers' institutes. 249 



returns from it, for it requires more and more each year to keep up the 

 standard of production.. Plants cannot obtain food even from fertiHzers 

 unless they have a well developed root system. Tliey can have such a 

 root system only when growing- in a mellow soil and permanent mellowness 

 is secured only by means of humus. These are facts that should be con- 

 stantly kept in mind by the farmer who begins the use of commercial fer- 

 tilizers. 



ANTITOXIN AND VACCINE. 



(By Dr. A. J. Detweiler, Bacteriologist and Sanitary Chemist of the State 



Board of Health.) 



Just at this time a discussion of these two subjects is of great im- 

 portance. I believe that the prejudice against the use of vaccine and anti- 

 toxin results from a lack of knowledge of their nature. Believing this to 

 be the case I shall briefly explain their nature in order that the farmers 

 may know why we expect good results in their use. I shall have to ex- 

 plain what we mean by a contagious or infectious disease, and the result- 

 ing immunity, before you will be able to vmderstand what we mean by 

 artificial immunity. 



A contagious or infectious disease is a disease contracted from a pre- 

 vious case of the same disease. Thus the disease spreads from one in- 

 individual to another, or from one animal to another. The ease with 

 which contagious or infectious diseases spread from individual to individ- 

 ual varies in different contagious or infectious diseases, and hence the 

 terms contagious and infectious. At one time a disease that spread only 

 on contact with a previous case was known as a contagious disease. A 

 disease contracted even when at a distance from a diseased body was 

 formerly known as an infectious disease. Thus we see that one infectious 

 disease might lead to hundreds or thousands of other cases. If this be 

 true the cause of the disease must be something capable of growth. Thus • 

 reasoning we were led to believe that infectious or contagious diseases 

 must be caused by some living cause, capable of growth and reproduc- 

 tion. This was believed long before we had any means of exact demon- 

 stration. Now we have discovered by means of the microscope and other 

 scientific means that disease is caused by parasites belonging both to 

 the animal and vegetable kingdoms. 



Only a few of our infectious diseases are caused by animal parasites 

 such as malaria, Texas fever among cattle, etc. However, there is a good 

 reason for believing that smallpox is also caused by a parasite which will 

 be classed in the animal kingdom. Of course these parasites are of a 



