A CONTRIBUTION TO THE MORPHOLOGY OF BACTERIA. 5 
probably it returns to an atavistic stage in its evolutional 
history. 
B. The second microbe, by which a similar marked change 
is exhibited, is the Bacillus diphtheriz. Loffler (‘ Mitth. 
aus d. k. Ges.,’ vol. 11) first drew attention to the fact that the 
diphtheria bacillus, discovered by Klebs, shows on cultivation 
a curious segregation of its protoplasm, and a knob-like or 
club-shaped enlargement of one or both ends. Léffler, and 
after him others (Fligge, ‘Mikroorganismen ;’ Baumgarten, 
‘Pathologische Mycologie,’ and others), considered these changes 
as due to involution. I have already, in the ‘ Report of the 
Medical Officer of the Local Government Board, 1889-90,’ and 
‘Centralblatt f. Bakt. und Parasitenkunde,’ vol. vii, 1890, 
shown that this view cannot be correct, for the following 
reasons : 
(a) In the diphtheritic membrane, in which the progress of 
the disease is still active, an abundance of diphtheria bacilli 
occur, which show this change in a marked degree, viz. segre- 
gation of the protoplasm into spherical, cubical, or cylindrical 
particles, and terminal knobs or clubs, sometimes of great 
size and containing vacuoles. 
(6) On agar cultures, already after twenty-four to thirty- 
six hours, when the growth is in its initial and most active 
phase, an abundance of bacilli are seen, which are shorter or 
longer threads, in which the segregation of the protoplasm and 
the terminal knobs and clubs are already very marked (fig. 4). 
(c) In the subcutaneous necrotic tumour of the cow, pro- 
duced by subcutaneous injection of virulent culture of the 
Bacillus diphtheriz, there occur connected masses and 
clumps in which at the growing margin the diphtheria bacilli 
appear all in the form of threads, in which the spherical or 
oval swellings and terminal knobs are most conspicuous, and 
strikingly resemble the ends of growing hyphe; the subjacent 
muscular fibres become invaded and gradually destroyed by 
the growth of the threads into their substance. This process 
of the gradual growth and penetration of the diphtheria 
threads with swellings and club-shaped ends into the muscular 
