ELEMENTARY PROBLEMS IN PHYSIOLOGY. 427 



Protoplasiu therefore (understamliug by the term the visible aud 

 tiingible preseiitatiou to our senses of living material) comes to consist 

 of two things, namely, of frame-work aud of content, — of chaunel and 

 of stream, — of acting part which lives and is stable, — of acted-on part 

 which has never lived and is labile, that is, in a state of metabolism, or 

 chemical transformatiou. 



If such be the relation between the living frame-wori^ aud the stream 

 v.iiich bathes it, we must attribute to this living, stable, acting part a 

 ])roperty which is characteristic; of the bodies called in physiological 

 language ferments or enzymes, the property which, following Berzelius, 

 we have for the last half century expressed by the word catalytic, 

 which we use, without thereby claiming to understand it, to indicate a 

 mode of action in which the ageut which produces the change does not 

 itself take part in the decomi>ositious which it produces. 



I have brought you to this point as the outcome of what we know as 

 to the essential nature of the all-important relation between oxygen 

 and life. In botanical physiology the general notion of a stable cata- 

 lysing frame- work, and of an interstitial labile material, which might be 

 called catalyte, has been arrived at on quite other grounds. This no- 

 tion is represented in i^lant physiology by two words, both of which 

 correspond in meaning, — Micelhe, the word devised by Niigeli, and the 

 better word, Tagmata, substituted for it by Pfeffer. Niigeli's word has 

 been adopted by Professor Sachs as the expression of his own thought 

 in relation to the ultra-microscopical structure of the protoplasm of the 

 plant cell. His view is that certain well-known properties of organized 

 bodies require for their explanation the admission that the simplest vis- 

 ible structure is itself made up of an arrangement of units of a far in- 

 ferior order of minuteness. It is these hypothetical units that Niigeli 

 has called Micellne. 



Now, Niigeli*, in the first instance, confounded the micelhe witli mole- 

 cules, conceiving that the molecule of living matter must be ol" enor- 

 mous size. But inasmuch as we have no reason for believing that any 

 form of living material is chemically homogeneous, it was soon recog- 

 nized, perhaps first by Pfeffer,+ but eventually also by Niigeli himself, 

 that a micella?, the ultimate element of living material, is not equiva- 

 lent to a molecule, however big or complex, but must rather be an 

 arrangement or phalanx of molecules of dilferent kinds. Hence the 

 word Tagma, first used by Pfefler, has come to be accepted as best ex- 

 l)ressing the notion. And here it must be noted that each of the physi- 

 iologists to whom reference has been made, regards the micelhe, not as 

 a mere aggregate of separate particles, but as connected together so as 

 to form a system ; — a conception which is in harmony with the view I 

 gave you just now from the side of animal physiology, of catalysing 

 frame- work and interstitial catalysable material. 



* Niigeli, "Theorie der Giibrnng,"' Beitrag sur Molecular Fhi/siologie, 1879, p. 121. 

 t Pfeffer, Pflanzcnphyniohgie, Leipsic, 1881, p. 12. 



