250 PHARMACEUTICAL BACTERIOLOGY 



of physiological salt solution and the centrifugal machine) and mix the 

 white corpuscles thus removed from the serum, with the bacterial emulsion 

 and incubate as before, none of the bacteria will be found within the 

 leucocyte. This test however merely proves that the blood serum influ- 

 ences phagocytosis or leucocytosis. In order to, prove that the action is 

 upon the bacteria rather than upon the leucocytes, the following test 

 is made. Use the serum free leucocytes as before, but instead of adding 

 the plain bacterial suspension, add to it a blood serum free from leucocytes. 

 Mix this bacterial suspension now containing serum with the leucocyte 

 suspension, incubate^ as before and it will be found that the leucocytes 

 again contain bacteria. The serum has in some way acted upon (sensi- 

 tized) the bacteria rendering them capable of being seized upon by the 

 leucocytes. The phenomenon may be compared to the preparation of 

 food by cooking. 



Opsonins are specific in action as indicated, are thermostabile, that is 

 they are not destroyed by a temperature of 55 C. Quantitatively they 

 are very variable. They may even disappear entirely from the blood, at 

 least temporarily. Relative quantitative phagocytosis indicates what 

 is known as the opsonic index, which may be determined as follows: 

 (Leishman's method). Mix equal parts of the fresh normal blood and a 

 bacterial suspension in normal salt solution and incubate for 30 minutes. 

 Prepare stained slide mounts and obtain an average of bacteria per leu- 

 cocyte. This will give the normal phagocytic index, given as i. If, 

 for example, the normal leucocyte count gives an average of ten staphy- 

 lococci per leucocyte, and a comparative count of a patient afflicted 

 with abscesses, gives an average of 2 staphylococci, then his opsonic index 

 would be 0.20, that is, .much below normal. 



The opsonic index may be raised by injecting carefully measured 

 quantities of killed cultures (bacterins) of the organisms of the infection. 

 However, satisfactory results have been obtained in a few cases only, as 

 in acne, in pneumonia, in tubercular infections, and in a few other infec- 

 tions. Certain bacterins have given excellent results as preventives, as 

 in typhoid, in plague, in tetanus, and some other diseases. 



c. Toxins, Antigens, Toxoids. Toxins are poisonous substances elab- 

 orated by bacteria and other pathogenic organisms, which possess the 

 property of inducing the development of antitoxin (an ti- bodies, immune 

 bodies) in the serum of the blood and in the body cells. The toxin is the 

 result of the activities of substances formed in bacteria, known as antigens, 

 which give rise to the anti-bodies (antitoxins). That is, the antigen 

 through some form of stimulation gives rise to substances which neutralize 

 the action of the toxins formed by the toxigenic bacteria. Red blood 

 corpuscles and perhaps also other body cells contain antigens. The toxins 



