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judgment as to tlie essential nature of that which we call 
“ life.” The mere historical retrospect of the various views 
which have been at different times entertained and published 
as to the nature of vitality, however brief and bald, would 
occupy no inconsiderable time, and I shall content myself here 
with a short discussion of the latest phases into which this 
question has entered ; while I must entirely omit all consider- 
ations relating to the subject, still a contested one, of the 
origin of living matter. 
We are, in fact, enabled with advantage to eschew all 
formal review of the theories and controversies of the older 
writers upon this subject, by taking as the basis of our argu- 
ment the now universally admitted fact that what we in 
general language call “ life,” is manifested only by the par- 
ticular form of matter to which the now familiar name of 
“ protoplasm ” is applied. Living bodies, however simple, are 
probably always in part composed of other substances than 
protoplasm ; and when at all complex they unquestionably are 
so. Still, it is certain that the phenomena to which the term 
“ vital ” can reasonably be applied, are invariably associated 
with the larger or smaller quantity of protoplasm present in 
the living organism. This, to use the apt phrase of Professor 
Huxley, is the “ physical basis ” of life ; and though opinions 
may differ as to the ultimate nature of the connection between 
this matter and the phenomena of vitality, it is necessary, in 
the first place, to very shortly consider the chief facts which 
we may be said to actually know about protoplasm, and to 
indicate any important points on which our knowledge is still 
defective. 
The first accurate knowledge which we may be said to 
possess as to protoplasm dates from the earlier part of this 
century, when Dujardin * pointed out that various of the 
lowly organised animals now included in the sub-kingdom 
Protozoa are composed of a semi-fluid, apparently structure- 
less, contractile substance, which he designated by the well- 
known name of “ sarcode.” The name of “ protoplasm ” 
was, ten years afterwards, given by Yon Mohlf to a similar 
substance found in the interior of the cells of plants ; and, still 
later. Max Schultze J accomplished a still further advance by 
* Becherches sur les Organism.es inferieurs : Ann. des Sci. Nat., Tom. V. 
1835. 
t Vermischte Schriften, Botan. Inhalts., 1848. 
I Organismus der Polythalamien, 1854 ; Miilleds Archiv, 1861 ; Das 
Protoplasma der Bhizopoden, 1863, 
