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Herpetomonas and Critliidia 
in structure between bacteria and flagellates is only relative because it 
refers to an abnormal structure of the flagellate compared with a normal 
structure of bacteria. I nevertheless believe that this similarity in 
structure may indicate a more than superficial relation between some 
flagellates and bacteria; Schaudinn (1902-1903) has already expressed 
the opinion that such a relation exists. It wmuld however be premature 
to base any far-reaching speculations on these isolated observations; 
I have mentioned them here only to draw attention to this interesting 
systematic cjuestion of the supposed mutual affinities of bacteria and 
flagellates. 
2. Degenerative appearance of some protozoa in relation, 
to Hertwig’s “physiological degeneration.” 
In the last two years much work has been done by the contributors 
to this Journal on the phenomena occurring during the degenei’atiou of 
some Haematozoa, e.g. Trypanosoma and Piroplasma. This work was 
originally undertaken with the object of clearing up certain errors in 
the interpretation of so-called sexual processes which had been described 
in the life-history of these organisms, but I think the facts now 
collected may serve as a base for a broader view. 
In 1882 Weissmann formulated his well-known theory on the 
immortality of unicellular organisms. The individual may divide and 
disappear in that way, also parts of the living cell may be thrown off or 
become destroyed, but death, i.e. destruction of the whole organism in 
another way than by formation of two or more daughter individuals, 
does not occur under normal (physiological) conditions. 
This theory was seriously contested by Hertwig (1904) who thinks 
that “ physiological death,” i.e. death originated by the vital functions 
themselves, occurs among unicellular organisms and so ma}^ be con- 
sidei'ed to be an intrinsic attribute of life. Only cells with reduced 
vital functions may live for an indefinite time (gametocytes). 
The cause of this physiological death is an abnormal relation 
between the nucleus and the protoplasm, leading to the so-called 
“ physiological degeneration,” and at last to death. Among unicellular 
organisms it may be prevented by encystment or conjugation, both 
processes leading to a reduction of the nuclear apparatus and thus 
re-establishing the normal relation between protoplasm and nucleus. 
If these regidating influences do not come into action, the “physio¬ 
logical degeneration ” begins. It is characterised by the hypertrophy 
