1864. | Samvuetson on the Source of Living Organisms. 599 
cation of some lower and preceding form of life, brought about solely 
by secondary causes, cannot halt midway in his teaching, and be 
content to hold that life began with four or five primitive types, such 
as he may be able to trace in the lowest inhabited strata; he must 
carry his investigations still further, and must account satisfactorily 
for the appearance of life-endowed beings in any shape, before he 
can be said to have fully established his position. 
It is in this spirit that the inquiry is now prosecuted ; and those 
who take a deep interest in the subject, do so, not as formerly, for the 
purpose of ascertaining from what source a particular group or 
species of animals is derived, but with an earnest desire to obtain 
some knowledge as to the conditions under which life is first mani- 
fested on the earth’s surface. Nor is the consideration of the subject 
confined to the ranks of biologists only, for some of the most important 
discoveries have already been made by chemists and physicists, and 
it is more than probable that the solution of the problem (should that 
follow in the course of time) will be due to the joint researches of 
men engaged in the study of these various branches of science, every 
one of which cannot fail to be indirectly benefited by the investi- 
gation. 
Probably the attention of reflecting observers was first directed to 
the subject of the origin of living beings through the mysterious 
appearance, in the decaying bodies of animals and elsewhere, of the 
larvee of insects; and the earliest treatise of any note on the subject 
was most likely that of Redi, ‘De Generatione Insectorum,’ Amster- 
dam, 1686, up to whose time it was currently believed that decaying 
substances became converted, during their decomposition, into insects 
and some other forms ranking below them in the animal scale, This 
is called ‘‘ spontaneous generation.” 
After the publication of Redi’s researches on the mode of repro- 
duction in insects, the theory of abnormal generation was for a time 
discarded ; but about sixty years subsequently, in 1745, Needham 
revived it in a work published in London, entitled ‘New Micro- 
scopical Discoveries ;’ and, on the other hand, about fifty years after 
that, another observer, Spallanzani, an Italian, attempted to disprove 
the existence of “spontaneous generation ” by experiments and philo- 
sophical induction. He sought to show that animalcule which make 
their appearance in decaying organic substances are not accidentally 
generated by the reconstruction and reorganization of such matters, 
but that their ova, er germs, exist in the atmosphere, and being con- 
veyed into the decaying substances, find in them a suitable pabulum, 
and thus become developed. He stated that if the air is excluded 
from such substances no animalcule make their appearance. 
This was the state of the discussion sixty or seventy years since ; 
and although considerable progress has no doubt been made in the 
inquiry, the field of research being necessarily more restricted than 
formerly, inasmuch as every day the appearance of some form or 
other is accounted for without any appeal to “ spontaneous generation,” 
still the elements of the dispute remain much the same as they were, 
and the chief efforts of investigators are directed to the proof or 
