THE BLOOD AS A LIVING TISSUE 



197 





^-r^, 



a 



are presently destroyed, being dissolved by a specific substance 

 that is capable of dissolving these foreign ce/Is. This cell- 

 dissolvmg siibsta7ice 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 

 of cells, as of different tissues or of 

 various bacteria ; and they are always 

 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- 

 teria will dissolve typhoid bacteria when 

 the two are mixed in a glass, but not 

 other species of bacteria. 



These facts are utilized practically in 

 vaccination against typhoid fever, and no 

 doubt other diseases will be found sus- 

 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). 



\ 



Fig. 74. Agglutination 

 of typhoid bacilli 



a, bacilli swimming about 

 separately ; b, the same 

 clumped together, or ag- 

 glutinated. The Widal test 

 for typhoid fever consists 

 in mixing a few drops of 

 serum from the suspected 

 person with a quantity of 

 typhoid bacteria under the 

 microscope. If agglutina- 

 tion takes place, the person 

 is known to be infected 

 with typhoid germs 



