390 FOODS CIRCULATED AND USED IN THE BODY 



Disease-resisting functions of the plasma. It is common 

 knowledge that some of us " take " catching or communicable 

 diseases more easily than others. Some fortunate persons are 

 immune to certain diseases, that is, they do not take them, because 

 certain antibodies are present in their blood. These antibodies 

 act in different ways, but their work is directed against bacteria 

 which get into the body and cause disease. Some antibodies, 

 called lysins, have the power to dissolve bacteria. Others, called 

 agglutinins, cause the bacteria in the blood to clump together in 



The diagram on the left shows free swimming typhoid bacteria. The diagram on the right 

 shows the bacteria clumped together by agglutinins which are produced by the body cells as 

 a protective measure. The bacteria are stationary and can be more easily destroyed by the 

 white corpuscles. 



little inactive masses, so that they are an easy prey for the phago- 

 cytes and lysins. We have already heard of the work of the 

 opsonins, another kind of antibody. Agglutinins and certain 

 other antibodies called -precipitins, which precipitate the bacteria 

 from solution, have become a great help to physicians in deter- 

 mining whether a person has a given disease. For example, a test 

 known as the Widal (ve-daT) test is now used in all hospitals to 

 determine if a person has typhoid fever. A few drops of blood 

 from the patient is allowed to stand until the serum has separated. 

 This is then diluted with a weak salt solution and to this are added 

 some living typhoid bacteria. If the person has typhoid, the 

 bacteria added to his serum will immediately become clumped 

 together or agglutinated, thus showing that his antibodies are 



