248 
POPULAR SCIENCE REVIEW. 
The fungologist recognises the same species of many fungi 
under various forms so discrepant that only a study of their life- 
history could lead to the belief that they were in any way 
related. Messrs. Dallinger and Drysdale show this to be the 
case with certain monads ; and probably a great many infusoria 
are able, at certain stages of their existence, to give rise to 
other forms, if the surrounding conditions are favourable. The 
yeast plant and allied fungi, according to M. Pasteur, are able 
to change their mode of living if introduced into new circum- 
stances, sufficiently young. In one state they are consumers of 
the oxygen of the air, but they can live in fluids containing 
none of that substance, and then their vital processes are carried 
on through the power they possess of decomposing bodies which 
contain it. He divides certain organisms into two classes : 
aerobies , which require air, and anaerobies , which can do without 
it, although capable of using it. The latter act as ferments 
when deprived of air, and join the aerobies , ceasing to be fer- 
ments when it is supplied to them. These opinions were 
contradicted by experiments of MM. Brefeld and Traube, but 
confirmed by fresh researches of M. Pasteur, who discovered 
that his opponents had, in one case, not employed young yeast 
cells, but only older cells, whose habits, so to speak, had become 
fixed ; and, in another, admitted extraneous bodies, which 
affected the result.* These observations may suggest important 
inquiries with reference to organisms supposed to cause disease. 
Besides the fungi mentioned by M. Pasteur, many other 
organisms may act as ferments, or not, according to their sur- 
roundings, and this may make all the difference between their 
innocence and their noxiousness. 
The researches of Messrs. Dallinger and Drysdale may well be 
considered in connection with facts like the preceding. They 
operated chiefly with an infusion of cod’s head, which produces 
after the ordinary forms that occur in putrefying matters, 
several remarkable monads. In some cases the creatures they 
describe did not appear until the infusion had been kept for 
many months. 
Their first observations related to the monad in PI. CXXIII., 
fig. 1 , which multiplied by transverse fission. First came an hour- 
glass constriction, and both ends of the little animal tugged 
away from each other until the sarcode at the thinner portion was 
stretched out to a fine thread, and finally snapped to make new 
flagella when the separation was completed. After this mode 
of division had gone on for a period extending from two to 
eight days, some of these monads became amoeboid, as shown in 
fig. 2, where they are beginning to coalesce. The coalescence 
* u Comptes Kendus,” Feb. 22, 1875. 
