THE BLOOD AS A LIVING TISSUE 



197 



are presently destroyed, being dissolved by a specific substance 

 that is capable of dissolving these foreign cells. This cell- 

 dissolving substance is not constantly present in the blood, but 

 is formed after the foreign cells are introduced. These cytoly- 

 sins, or "cell dissolvers," are formed not only in response to 

 the foreign red corpuscles ; they may be 

 formed in the presence of other kinds ~ i .j*XC x o, 



of cells, as of different tissues or of >/7'Jr l K\ 



various bacteria; and they are always *"-^r i-N'^"* 



specific. Thus, the serum of a rabbit 

 that has been treated with human blood 

 will dissolve the red corpuscles of human 

 blood when the two are mixed in a glass, 

 but not the corpuscles of any other ani- 

 mal. The serum of a person whose blood 

 has been treated with dead typhoid bac- a> bacilli swimming about 

 teria will dissolve typhoid bacteria when separately; 6, the same 

 the two are mixed in a glass, but not dumped together ' or ag ' 



b 



FIG. 74. Agglutination 

 of typhoid bacilli 



other species of bacteria. 



tion takes place, the person 

 is known to be infected 

 with typhoid germs 



glutinated. The Wtdal test 

 for typhoid fever consists 

 T-I / ,-T i .. 11 . in mixing a few drops of 



These facts are utilized practically in serum from the susp ^ cted 

 vaccination against typhoid fever, and no person with a quantity of 



i,, ,1 j. MI i r j typhoid bacteria under the 



doubt other diseases will be found sus- mi cr sco pe . if aggiutina- 



ceptible to the treatment. A measured 



quantity of dead typhoid germs is injected 



into the body. The specific cytolysin is 



formed by the action of the live cells. Later, when live 



typhoid germs get into the body, they are dissolved by the 



cytolysin already present. 



Recently a specific cytolysin active against the cells that cause 

 cerebrospinal meningitis has been produced experimentally in monkeys 

 by Dr. Simon Flexner of New York, and the serum of these animals 

 may be successfully used in treating the disease in human beings. 



The cytolysis test may also be used like the precipitin test 

 in the differentiation of blood stains etc. (see p. 194). 



