THE NOTION OF SPECIES 3 



Each series includes a certain number of terms (entities) 

 which differ from each other by the value of n ; for instance, 

 to the acetic series belong the glycerides of 



acetic acid (C2H4O2), 

 butyric acid (C4H8O2), 

 caproic acid (CeHigOa), 

 lignoceric acid (C24H48O2), etc. ; 



to the acrylic series belong the glycerides of 



tiglic acid (CgHgOg), 



oleic acid (C18H34O2), 



enicic acid (C22H42O2), etc., etc.^ 



Between the terms of each series and also between the series 

 of a given group evident analogies exist, not only with regard 

 to the chemical constitution, but also in the fades and physical 

 properties. 



(2) The PROTEINS 2 seem to be polypeptides which are 

 formed by the conjugation of a large number of amino acids. 

 Altogether more than fifty proteins are known to occur natur- 

 ally in animals and plants, which differ from one another in 

 physical and chemical properties. They may be brought into 

 classes and groups in the following way ^ : — 



Class A : Simple Proteins. 



Group I : Protamines. 



„ 2 : Hist ones. 



„ 3 : Albumins. 



„ 4 : Globulins. 



„ 5 : Prolamins (Gliadins). 



„ 6 : Glutelins. 



„ 7 : Scleroproteins. 

 Class B : Conjugated Proteins. 



Group 8 : Nucleoproteins. 



„ 9 : Glycoproteins. 



„ 10 : Haemoglobins. 



„ II : Phosphoproteins. 



„ 12 : Lipoproteins. 

 Class C : Derived Proteins. 



Group 13 : Proteans (Metaproteins) . 



„ 14 : Coagulated Proteins. 



„ 15 : Proteoses. 



„ 16 : Peptones. 



„ 17 : Peptides. 



^ THORPE, loc. cit., vol. iii., p. 744. ' Ihid., vol. iv. (1913), p. 407. 



' The classification here given is adopted by American physiologists and 

 chemists. See Thorpe, loc. cit., vol. iv. 



