136 BACTERIOLOGY OF MEAT AND MEAT PRODUCTS 



B. Material from Jiuuian cases. The examination of materials 

 from autopsies is conducted in a similar manner but is usually 

 much easier, the bacilli being frequently present in pure or 

 nearly pure culture. Only a few L.B.A. and other plates need 

 to be inoculated from each organ. Frequently the presence of 

 Gaertner group bacilli can be demonstrated within 24 hours. 



The testing of the agglutinative properties of the blood of 

 actual or suspected cases is a very important part of the investi- 

 gation, and even when no other material at all is available for 

 examination is sometimes sufficient to accurately determine the 

 cause of infection. 



The sera must be tested against stock cultures, at least 

 B. enteritidis and B. suipestifer being used for each specimen. 

 Low dilutions, i.e. I : 30, should be used for the first test and, if 

 positive, then the serum tested to the limit of agglutination. 



If possible a little of the serum should be retained to test 

 against any Gaertner group bacilli isolated from the food or 

 post-mortem materials. 



CHAPTER IX 



AIR 



Bacteria are always present in air, but, unless the air con- 

 tains a large number of dust particles, in comparatively scanty 

 numbers. 



It is not that they are not discharged into the air, but rather 

 that they do not thrive in it. Bacteria are constantly being 

 wafted from dry surfaces, and in this way considerable numbers 

 gain access to air and, owing to their lightness, are carried con- 

 siderable distances. Unlike soil, milk, water, etc., air does not 

 serve as a food for bacteria, and they do not multiply in it. On 

 the other hand, there are a large number of agencies at work 

 which diminish the number of organisms which have gained 

 access to air. Of these the most important are the germicidal 

 action of light, especially sunlight, and the action of gravity. 



Pathogenic organisms are not readily detected in air, the 



