PHAGES AS ANTIGENS 



341 



Fig. 53. 



Differentiation of phage types by their action on 

 resistant bacteria. 



lysis over the circular area inoculated with the 



growth from our Type II phage, 

 over the squares in the third column 

 the secondary growth from our 

 Type III phage, and over the squares 

 in the fourth and last column 

 the secondary growth from the 

 culture containing all three phages. 

 Then we take a filtrate containing 

 Type I phage, and spread a small 

 drop of it over a circular area in the 

 middle of the top square of each 

 column {i.e. of each square of the 

 first row). In each square of the 

 second row we make a similar in- 

 oculation of Type II phage, in each 

 square of the third row an inocula- 

 tion of Type III phage, and in each 

 square of the fourth and last row, an 

 inoculation of phages I, II and III. 



If the phages actually belong 

 to different types, as judged by this 

 test, the results will be as shown in 

 Fig. 53, in which the dark circles 

 indicate the occurrence of confluent 

 phage. 



It will be noted that Phage I acts on the secondary growth from Phages II and III, 

 but not on the secondary growth from Phage I, and so on. None of the three phages 

 acts on the secondary growth from the culture submitted to the action of all three phages. 

 The mixture of three phages acts on the secondary growth from each of the three separate 

 phages. 



If we desire to test another phage, to see whether or not it is identical with any of our 

 three Types I, II, or III, we include it in such a series of tests, addmg the additional row 

 and column to our squares. If it is identical with any of our three types it will behave 

 as that type does. If it is a new type (say Type IV) then it will lyse the secondary growths 

 from Types I, II and III, and its own secondary growth will be lysed by each of these 

 types. 



This leads us to a consideration of other ways in which phages may be 

 differentiated from one another. One of these is the method of antigenic analysis, 

 which has been so extensively employed in the identification and classification 

 of bacteria. 



Phages as Antigens. The Phage-Antiphage Reaction. 



It was shown by Bordet and Ciuca (1921) that the phage is antigenic, and that 

 an antiphage serum has the power of neutralizing the phage and so preventing its 

 lytic action on bacteria. Numerous workers have since studied this phenomenon, 

 and it has been clearly shown (a) that the inhibition of phage lysis is due to anti- 

 bodies acting on the phage itself, and not to the antibacterial antibodies that are 

 usually present in an antiphage serum, (6) that the antibodies are specific for 

 particular types of phage, phages thus showing an antigenic specificity of exactly 

 the same kind as that displayed by bacteria, but (c) that the antibodies have.no 

 action on the bacteria from which the phage arose ; that is, phage and bacterial 

 host are serologically distinct. Many of the papers already referred to contain 



