600 Original Articles. ; | Oct., 
disproof of the existence of the germs of living beings in the atmo- 
sphere. 
: The clearest and most tangible exposition of the views of those 
who formerly advocated the theory of heterogenesis, or abnormal 
generation, is to be found in Todd and Bowman’s ‘ Cyclopedia of 
Physiology,’ in the edition published in 1839 ;* and it will be found 
useful for our purpose to extract some of the writer’s remarks, inasmuch 
as they will show the student of to-day how the recent revelations of 
science have struck away, one by one, the props upon which the doc- 
trine was based, and have so reduced the inquiry within the narrowest 
limits. 
‘‘ The following considerations appear to us to throw the balance of 
evidence in favour of the spontaneous production of infusoria, mould, and 
the like. Firstly, those organic matters which are most soluble in water, 
and at the same time most prone to decomposition, give rise to the 
greatest quantity of animalcules or cryptogamic plants. Secondly, the 
nature of the animalcule or vegetable production bears a constant relation 
to the state of the infusion; so that, in similar circumstances, the same 
are always produced without this being influenced by the atmosphere. 
There seems also to be a certain progressive advance in the productive 
powers of the infusion, for at first the animalcules are only of the smallest 
kinds, or monads, and afterwards they become gradually larger and more 
complicated in their structure: after a time the production ceases, 
although the materials are by no means exhausted. When the quantity 
of water is very small, and the organic matter abundant, the production 
is usually of a vegetable nature ; when there is*much water, animalcules 
are more frequently produced. Thirdly, on the supposition that infusory 
animalcules are developed from ova, it is necessary to conclude, from the 
experiments already referred to, that these ova are in some instances 
derived from the atmosphere ; but yet the number of infusoria is by no 
means in proportion with the quantity of air. We are also reduced to 
the necessity of holding that every portion of the atmospheric air is 
equally impregnated with infusorial germs or ova, and that these bodies 
may remain for years dissolved, as it were, or invisibly suspended in the 
atmosphere, and in a perfectly dry state,—a supposition contrary to 
analogy, and not fully warranted by the fact that vibriones may be resus- 
citated by means of moisture after they have been kept in a dry state for 
long periods. Fourthly, it may be remarked that the existence of ova, 
as belonging to many of the infusoria, is entirely hypothetical, since most 
of these animals are known, when once formed, to propagate by other 
means, as by the division of their whole bodies, or by budding.” 
If the writer of these remarks had been aware when he penned 
them (and we hope he still lives to witness the results of scientific 
progress since his observations were made), that the same general laws 
which regulate the growth and development of the higher animals 
are found to operate very low down in the scale, he would not have 
leaped to such conclusions. The rapid increase of animalcules in 
substances “ most prone to decomposition,” would merely have satisfied 
him that the abundance or scarcity of living forms in infusions was 
* In which the student will also find additional information concerning the 
history of the controversy. 
