io METABOLISM 



accomplished, and to the predominance of the chemical over the mechanical 

 processes taking place in protoplasm, it is perhaps on the whole more appro- 

 priate to institute a comparison between protoplasm and a chemical laboratory 

 or manufactory. In such a manufactory many chemical operations are carried 

 out, possibly in the same room ; but many of these operations must be kept 

 entirely apart if the wished-for result is to be attained. So also within a single 

 cell both oxidation and reduction, anabolism and katabolism of protoplasm 

 may take place, and for this reason alone organization in the protoplasmic 

 body is essential, since conflicting operations must be kept isolated. F. HOF- 

 MEISTER (1901) has drawn attention to the fact that, looked at from this point 

 of view, an alveolar structure in the protoplasm may have a deep significance. 

 Every one of the countless cavities might be considered as a chamber cut off 

 temporarily or permanently from the exterior. Within the space of a cubic 

 /i the most heterogeneous reactions may take place. The aim of future 

 research must be, without over emphasizing either the material of which proto- 

 plasm is composed or its organization, to take both of these phenomena into 

 consideration, and to employ them as bases for wider research in this most 

 difficult subject. At the same time it may be expressly noted that purely 

 chemical research into the nature of protoplasm is by no means valueless, 

 and that it has not yet been shown that chemical peculiarities play no part in 

 protoplasmic phenomena. It is obvious that we have not as yet discovered 

 any living chemical compound or any mixture of chemical compounds which 

 may be considered as vitally active, since the physiological chemist must of 

 necessity kill the very living substance he desires to study in subjecting it to 

 analysis. Experiments in physiological chemistry have shown sufficiently that 

 in proteids we are dealing with substances not only exceedingly complex but 

 also very delicate and labile, substances which may become continually altered 

 owing to apparently quite trifling causes. One can scarcely doubt that the 

 transformations which are exhibited by protoplasm, e. g. through the influence 

 of gentle pressure, and which result in local or general death, depend not merely 

 on changes in organization but also on chemical changes which are irreparable. 

 Thus chemical alterations are set up if water enters a protoplasmic particle 

 previously surrounded by salt solution, and these alterations may be expected 

 to be even more pronounced when the contents of two alveoli or two vacuoles, 

 originally separate, become united. REINKE (1901) says that ' if one gently 

 bruises in a mortar some pure protoplasmic rudiments of fruits of Mycetozoa, 

 the substance remains unaltered quantitatively and, to all appearance, also 

 chemically, but its organization is irretrievably destroyed, so that subsequent 

 differentiation of fruits is completely inhibited ; in other words, the protoplasm 

 is killed by the pestle without chemical action of any sort'. This view we 

 cannot agree with, for although the rubbing in the mortar may not, it is true, 

 have affected the substances enumerated in the analysis given above, still the 

 albumins and phosphorus-containing proteids must have been greatly modified. 



The data we have obtained as to the chemical composition and structure 

 of protoplasm are applicable not only to protoplasm as a whole, but individually 

 also to cytoplasm, nucleoplasm, and chloroplasts. Since the nucleus and chroma- 

 tophores are living parts of the plant they may be considered as organs of the 

 protoplasm. From the chemical standpoint there are many agreements as well 

 as many differences between the cytoplasm and the nucleoplasm, but we need 

 not follow out these in further detail at this stage, since they have not as yet 

 been shown to have any general physiological significance. For the same 

 reason we may omit here any reference to the results obtained from investi- 

 gations into the chemistry of the proteids. It is to be hoped, however, that 

 these results may soon prove to be of greater physiological value than heretofore. 



To summarize, therefore, it may be said that our first attempt to obtain 



