1864. SamuEtson on the Source of Living Orqanisms. 601 
g Urg 
in proportion to the amount of nourishment afforded to them; and in 
the appearance of certain characteristic types in particular infusions, 
he would have recognized the operation of the law which causes every 
plant (speaking in general terms) to be peopled by its appropriate 
parasite. His statement that the same animalcule are always found 
in similar infusions, is however only partially correct, and, as it will 
be shown hereafter, is far from being a correct phenomenon. 
Next, as regards the “progressive advance in the productive powers 
of the infusion,” the appearance in fact of successive generations of 
living forms rising in the developmental scale, in one and the same 
infusion. An acquaintance with the phenomena of the “alternation 
of generations,” and a little reflection upon the fact that “ Monads ” 
may grow into ciliated infusoria whilst the eye of the observer is 
engaged otherwise than in their examination, would have materially 
shaken the writer’s faith in the “‘ productive powers” of the infusion. 
The researches of my esteemed coadjutor, Dr. Balbiani, of Paris, 
have set at rest the question of the existence of ova in the infusoria, 
for he has shown that in addition to the other processes by which they 
multiply, these forms possess also the sexual elements common to all 
animals, * 
The only question, therefore, of any importance to which a satis- 
factory reply is required, is the one already referred to:— Do the 
germs of infusoria, or do they not, exist in the atmosphere in sufficient 
quantities to account for their entrance into infusions ? 
Before proceeding to consider this vital question, however, it is 
right that I should touch upon a phenomenon referred to by the 
writer in “ Bowman” in another part of his article, and thrown by 
him into the scale in favour of the theory of heterogenesis. That 
is, the appearance of entozoa, or internal parasites, in the tissues 
(or, as he says, the bodies) of living animals. This is really a most 
difficult problem to solve, but we never hear it mentioned at the 
present day even by the advocates of heterogenesis. The presence of 
some of these parasites is still a great mystery, on which a partial light 
only has been thrown by the recent researches of zoologists in regard 
to the transformations that such forms undergo in their passage from 
one animal into another, from the prey into the stomach, and then into 
the vascular, or other systems of its devourer. As already observed, the 
advocates of the doctrine under consideration do not now affirm that 
any of these forms are spontaneously produced from the living tissues 
in which they are found; and I believe that at no very distant 
period their presence will be, in all cases, fully accounted for. 
The chief investigators who have recently asserted that the 
germs of living beings do noé exist in the atmosphere, or that they 
exist only in such small quantities as to render it impossible that the 
swarms of animalcule which appear in infusions should be derived 
from that source, are—Messieurs. Pouchet, Jolly, and Musset 
(France); Dr. Jeffries Wyman, of Boston (America); Schaffhausen 
* * Recherches sur les Phénomenes sexuels des Infusoires,’ par le Docteur 
A. Balbiani. Paris: Masson. 1863. 
