Life History of Monads. By W. H. Ballinger cj- J. Drysdale. 189 
applies to Bacterium termo and Penicillium glaucum; but in the 
present state of our knowledge we may be allowed to infer that the 
sporules of these are simply ubiquitous. 
These simple reasons may quite sufficiently account for the 
successive appearance of different forms of infusoria in organic 
infusions, without having recourse to the startling hypothesis of 
heterogenesis. The reported observations of Dr. Bastian, Dr. Gros, 
and some few others, alleging the origination of one known form 
from parents of an entirely different nature, such as the develop- 
ment of nematoids from spores of vaucheria,* of diatoms, pedia- 
strieae and other algae from euglenae,t and so forth, are instances 
which we presume could only be accepted scientifically by tracing 
the whole process step by step, repeatedly, until every stage in the 
process of mutation was actually discovered and described. The 
possibility of misinterpretation is great. Indeed, we distrust all 
observations founded on successive “ dips ” in a quickly changing 
organic infusion, and in fact put no faith in observations of this 
sort not conducted on the plan of keeping the same drop under 
continuous observation during all alleged transformations. As far 
as our observations upon these lowly forms go, we are bound to say 
that not the slightest countenance is given to this doctrine of 
heterogenesis. On the contrary, the life cycle of a monad is as 
rigidly circumscribed within defined limits as that of a mollusc or 
a bird. There is no indication of any unusual or more intense 
methods of specific mutation than those resulting from the secular 
processes involved in the Darwinian law, which is held to furnish 
the only legitimate theory of the origin of species. 
In the facts pointed out in the previous pages we also see an 
explanation of the sameness which Billroth attributes to the 
organisms of the septic processes : he remarks frequently on the 
recurrence of so small a number or variety of generic forms in all 
putrefactive processes. He says, for example : “ The notion is 
widely prevalent that the minute organisms generally met with 
in the putrefaction of the juices of the human body form an 
impassable labyrinth, and belong partly to the animal and partly 
to the vegetable kingdom ; and also that in infusions of various 
organic tissues a countless multitude of so-called infusoria are 
found, with endless variety of form and species. But if anyone 
sets about looking into the wonders of the creation he is very soon 
undeceived ; instead of the expected variety, he finds a monotony 
of forms which soon extinguishes all interest of a merely superficial 
nature, for he may search various putrefying fluids for weeks without 
finding anything but what he was already familiar with in the 
first days of his microscopical studies, as vibriones, bacteria, and 
* ‘ Beginnings of Life,’ p. 531. t Ibid., p. 447. 
