SOME REPRESENTATIVE VIRUS DISEASES 41 
of growth, occasional cells began to show signs of swelling, and by the 
end of the third hour the great majority of cells in the field appeared more 
or less swollen, a few among them reaching several times their normal 
dimensions. Filaments swelled as well as ordinary bacteria. The swelling 
continued slowly until about the fifth hour, when, one by one, bacteria 
began to disappear suddenly and quickly. 
Before leaving the bacterial virus diseases it will be of interest to 
refer to the most recent work by Wyckoff (1948) who examined the 
lysis of bacteria by viruses with the aid of the electron microscope. 
He found that the phenomena accompanying lysis depended in 
striking fashion on the strain of bacteriophage. Sometimes the 
fragments of lysed bacteria are of a granular texture, but much of 
the protoplasm freed by lysis seems to be filamentous. Photographs 
taken, at a magnification of about 40,000, of a colon bacillus infected 
with T, strain of bacteriophage show a regular pattern of concavities 
extending over the entire surface of the organism. 

