20 INFECTIVE AND CONTAGIOUS DISEASES. 
cultivating solutions. Bacteria have been largely investigated, 
notably by Cohn, Bollinger, Billroth, Ewart, and Klebs. Cohn's 
classification in 1872 is now found to be of doubtful value. His 
definition of Bacteria is good, and we may for convenience describe 
them as assuming various forms— spheroidal, rod-shaped, bacilli- 
form, spirilliform, &c. The simplest of them are the spheroidal 
or globular, known as micrococci or microsporon, leading to the 
formation of zoogloea or mycoderma by aggregation, or becoming 
united in chains resulting from transverse division, as may be 
well seen in decomposing blood and aqueous humour. Some¬ 
times they divide transversely as well as longitudinally, producing 
groups of fours. Klebs, Billroth, and Dallinger believe these 
micrococci can become converted into the rod-shaped form or true 
Bacteria, but the lecturer has not been able to trace this. He 
believes that some micrococci never pass beyond the spheroidal 
stage. M. vaccince and M. diphthericus are some of the supposed 
pathogenic forms of micrococci. The rod-shaped form or bac¬ 
terium proper is usually flagellated or ciliated, and often presents 
nuclei or spores. Ewart has found these in B. termo ; it presents 
alternate stages of rest and motion, and forms zoogloea masses 
with a permanent and abundant intercellular substance. Filamen¬ 
tous Bacteria or Bacilli of one form occur in anthrax; and 
Koch and the lecturer have observed another very different in 
septicsemia of the lower animals. 
The lecturer has also recently observed a Bacillus in farcy. 
It resembles in its general characters Bac. anthracis , as described 
especially by Ewart, and presents the appearance of a lateral for¬ 
mation of spores, which may be arranged in pairs; they escape or 
are set free by the breaking up of the filament. Sometimes separate 
couples of spores result, and a large convoluted chain-like form 
has been observed. Also the spores sometimes divide into fours. 
The filaments are aggregated in masses, and each has a looped 
arrangement. (These remarks were illustrated by diagrams, to 
scale, executed from the lecturer's specimens.) In the Bacilli 
the spore develops into the filament. Klein, Koch, and Ewart 
have described this, but the observers differ as to the details of 
the process, it not being decided whether the spore itself elongates 
or its chitine-like investment. The Bacilli of septicsemia first 
elongate and divide transversely into pairs. Masses of these 
occur, with nuclei generally at the ends, but sometimes centrally 
placed. The filaments further elongate and then break up. In 
collections of this form, as in B. termo, rods are generally seen at 
the outerpart radiating from the centre where the spores are 
situated. 
The lecturer then proceeded to touch upon methods of 
investigation . Given a specific disease such as smallpox: It is 
