THE president's ADDRESS. 343 



white of egg, but this is a protein of comparatively simple 

 chemical structure ; many other proteins are much more com- 

 plicated in this respect, and contain a vast number of atoms of 

 several kinds combined together, those of most common occurrence 

 being carbon, oxygen, hydrogen, nitrogen, sulphur and phos- 

 phorus. Proteins are, in short, chemical compounds of such 

 complex nature that at the present time they are quite beyond 

 exact chemical analysis ; it is impossible either to state exactly 

 how they are built up out of their constituent atoms, or to make 

 them artificially in the laboratory. Proteins are characteristic 

 components of living bodies and can only be obtained from living 

 bodies. The enormous chemical complexity of proteins admits of 

 endless variations in them ; apparently every species of organism 

 has its own peculiar proteins, different from those of every 

 other species. * 



There is a further difficulty with regard to the chemical compo- 

 sition of the living substance. The chemist can only deal with it 

 when it is dead ; he must begin his analysis by destroying the 

 life. From the dead protoplasm a great number of different 

 proteins are obtained ; but it is impossible to state whether the 

 proteins existed separately as such in the living body, or whether 

 they were combined together into a far more complex substance. 

 We cannot say at the present time whether the essential 

 constituent of living matter is a single chemical substance or a 

 mixture or combination of various chemical substances; though 

 from the facts to be considered presently it seems more probable 

 that the second alternative is the true one, and that there is no 

 single chemical substance which could conceivably be isolated in 

 a pure state and be exhibited as the living suhstsmce par excellence. 

 In other words, the properties of living things are not to be 

 regarded as inherent in one single chemical compound ; from a 

 strictly chemical standpoint there is no living substance. 



Let us now consider briefly the physical and structural 

 peculiarities of protoplasm. Taken as a whole, protoplasm is 

 distinctly of a fluid nature ; it may contain particles or structures 

 of a firm consistence, but this does not prevent it being fluid in 

 the aggregate. Some samples of protoplasm may be less fluid 

 than others ; some are very distinctly and obviously fluid, others 

 may be stiffened to a degree that approaches very nearly to the 

 solid condition, lying on the boundary between fluid and solid 



