Dallinger engaged in long experiments watching various microbes through all
their developmental stages. Like Ferdinand Cohn, his contemporary, Dallinger
believed that one should observe the developmental cycle of an organism to demonstrate that species were stable. He was assisted in this work by his friend from the
Liverpool Microscopical Club, the physician John James Drysdale. Dallinger
corresponded with Darwin about his work, and Darwin wrote back saying:
Allow me to add that I have read all your [Dallinger] & Dr. Drysdale’s papers, & they seem
to me to possess higher value than anything that has been published on such subjects, though
I am too ignorant to have any right to express such an opinion. But I have a full right to say
that they are extremely interesting. (Darwin Correspondence Project Letter no. 10354
2020d)
In 1878 Dallinger began preliminary studies to address the question whether it is
possible to “superinduce” adaptive changes in a microbe by increasing the temperature of its environment. His efforts predated slightly later studies, described above,
by Beijerinck. Dallinger did not believe it was necessary to provide a direct demonstration of Darwin’s “great law,” but he felt that, “if it be possible to look upon the
progress of changes in minute living organisms, superinduced by elected changes of
environment, however, simple, and which results in morphological and physiological adaptations and survivals, it cannot be other than a gain both to philosophical
and practical biology” (Dallinger 1887a). He wrote to Darwin describing the results
of this preliminary study and Darwin replied:
I did not know that you were attending to the mutation of the lower organisms under changed
conditions of life; and your results, I have no doubt, will be extremely curious and valuable.
The fact which you mentioned about their being adapted to certain temperatures, but
becoming gradually accustomed to much higher ones, is very remarkable. It explains the
existence of algae in hot springs. How extremely interesting an examination under high
powers on the spot, of the mud of such springs would be. (Dallinger 1887a citing a Darwin
letter dated July 2, 1878)
Encouraged by Darwin, Dallinger then undertook a 7-year study of the adaptation of
the flagellated algae Tetramitus rostratus, the protozoan Monas dallingeri, and the
protozoan Dallingeria drysdali to increasing temperatures in a specially constructed
thermal bath (Fig. 2.11). He found he could increase their temperature of growth
from 69
F (20.5
C) to 158
F (70
C) by small increases in temperature over
several years. Tragically, the experiment ended through an accident that occurred
while he was away. He was not convinced that he had achieved the highest
temperature that he could and, following an understandable period of depression
over the incident, he finally decided to repeat the work (Dallinger 1887a). His initial
results proved Darwin’s contention that organisms could adapt to changing conditions. Further, since the organisms that had adapted to the highest temperature could
no longer grow at the original temperature, he showed that they had undergone a
permanent change, much like Darwin predicted should happen due to natural
selection. Dillinger had, for the first time, demonstrated Darwin’s theory of Natural
Selection.
Unfortunately, it seems that he did not carry the second effort to completion. He
apparently abandoned the effort and then took up work on technical aspects of
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
45
their developmental stages. Like Ferdinand Cohn, his contemporary, Dallinger
believed that one should observe the developmental cycle of an organism to demonstrate that species were stable. He was assisted in this work by his friend from the
Liverpool Microscopical Club, the physician John James Drysdale. Dallinger
corresponded with Darwin about his work, and Darwin wrote back saying:
Allow me to add that I have read all your [Dallinger] & Dr. Drysdale’s papers, & they seem
to me to possess higher value than anything that has been published on such subjects, though
I am too ignorant to have any right to express such an opinion. But I have a full right to say
that they are extremely interesting. (Darwin Correspondence Project Letter no. 10354
2020d)
In 1878 Dallinger began preliminary studies to address the question whether it is
possible to “superinduce” adaptive changes in a microbe by increasing the temperature of its environment. His efforts predated slightly later studies, described above,
by Beijerinck. Dallinger did not believe it was necessary to provide a direct demonstration of Darwin’s “great law,” but he felt that, “if it be possible to look upon the
progress of changes in minute living organisms, superinduced by elected changes of
environment, however, simple, and which results in morphological and physiological adaptations and survivals, it cannot be other than a gain both to philosophical
and practical biology” (Dallinger 1887a). He wrote to Darwin describing the results
of this preliminary study and Darwin replied:
I did not know that you were attending to the mutation of the lower organisms under changed
conditions of life; and your results, I have no doubt, will be extremely curious and valuable.
The fact which you mentioned about their being adapted to certain temperatures, but
becoming gradually accustomed to much higher ones, is very remarkable. It explains the
existence of algae in hot springs. How extremely interesting an examination under high
powers on the spot, of the mud of such springs would be. (Dallinger 1887a citing a Darwin
letter dated July 2, 1878)
Encouraged by Darwin, Dallinger then undertook a 7-year study of the adaptation of
the flagellated algae Tetramitus rostratus, the protozoan Monas dallingeri, and the
protozoan Dallingeria drysdali to increasing temperatures in a specially constructed
thermal bath (Fig. 2.11). He found he could increase their temperature of growth
from 69
F (20.5
C) to 158
F (70
C) by small increases in temperature over
several years. Tragically, the experiment ended through an accident that occurred
while he was away. He was not convinced that he had achieved the highest
temperature that he could and, following an understandable period of depression
over the incident, he finally decided to repeat the work (Dallinger 1887a). His initial
results proved Darwin’s contention that organisms could adapt to changing conditions. Further, since the organisms that had adapted to the highest temperature could
no longer grow at the original temperature, he showed that they had undergone a
permanent change, much like Darwin predicted should happen due to natural
selection. Dillinger had, for the first time, demonstrated Darwin’s theory of Natural
Selection.
Unfortunately, it seems that he did not carry the second effort to completion. He
apparently abandoned the effort and then took up work on technical aspects of
2 Darwin’s Science’s Impact on the Evolution of the Microbiological Sciences
45