THE NOTION OF SPECIES 5 



§ 6. — The facts stated in the preceding paragraph may be 

 summarized in the following way : — a large number of natural 

 substances are mixtures, consisting in the main of chemical 

 entities which belong to one chemical family ; the components 

 are associated in a different way in each species and each com- 

 ponent may occur in a certain number of specific mixtures. 

 On the other hand, the proteins may be looked upon as belong- 

 ing to a single chemical family. 



We may therefore accept the suggestion that Mving substance 

 (the living contents of the cell) follows the ordinary rule and is 

 a mixture, and since many well-known facts point to a chemical 

 relation between Mving substance and proteins, we may admit 

 that the components of the former are proteins — or substances 

 which are related to the already known proteins and which 

 might be called Bioproteins. 



The properties ^ of hving substance are, indeed, so character- 

 istic that we are, as it were, compelled to think that its com- 

 ponents are not merely proteins properly so called. It may be 

 suggested that these components are proteins of a pecuHar 

 kind, which deserve to be distinguished under the name bio- 

 proteins. 



It may be further surmised that the molecules of the bio- 

 proteins are more complex than those of the proteins, and are 

 formed by the conjugation of a larger number of amino acids,^ 

 the proteins properly so called being hydroUtic degradation 

 products of the bioproteins. According to this, a special class, 

 under the name of bioproteins, ought perhaps to be added to 

 the three classes mentioned in the classification adopted in § 5. 



§ 7. — The living mixture which is found in a cell or a Plas- 

 modium does not consist entirely of a homogeneous association 

 of components. Certain components are permanently or 

 temporarily separated from the others, being localized among 

 the hving mass ^ and differentiated in the form of nucleus, 

 chromosomes, centrosomes, protoplasmic granulations and, in 

 general, plastids. The differentiated parts may be themselves 

 mixtures of several bioproteins. It is quite possible that 

 a chromosome, for instance, is a compMcated mixture of a 

 number of bioproteic entities. A minute globule of cow butter, 



• Contractility ; semipermeability ; division of nucleus and plastids ; 

 irritability, etc. 



' Or by the conjugation of two or several already discovered proteins. 



" Example : Nucleoproteins (see p. 3, Group 8), which are compounds of 

 the strongly basic protamines (p. 3, Group i) with nucleic acid, seem to 

 be localized in the cell nucleus (Thorpe, loc. cil., vol. iv., p. 411). I do not 

 look upon nucleoproteins as being bioproteins. Certain bioproteins, how- 

 ever, may be localized in certain parts 01 the cell in the same way as nucleo- 

 proteins. 



