4 THE QUANTITATIVE METHOD IN BIOLOGY 



In each group we find a certain number of substances ; for 

 instance : 



In Group 3 (Albumins) : Legumelin, Leucosine, Ricin. 



In Group 4 (Globulins) : Amandin, Avenalin, Castanin, 

 Conglutin, Corylin, Edestin, Excelsin, Globulin, Myosin, Ovo- 

 globin. Fibrinogen, etc. 



Since the way in which the highly complicated molecules of 

 the proteins are built up is very incompletely known, their 

 classification is more or less of an empirical nature. There 

 exist, however, between those substances physical and 

 chemical analogies enough to justify the conclusion that they 

 are related to each other, at least to a certain degree, in a 

 similar way as the glycerides. 



(3) We find in the body of living beings, independently of the 

 living substance, numerous so-called substances the composi- 

 tion of which is more or less completely known. Many of 

 those substances are mixtures of several distinct chemical 

 entities. It is, from a biological standpoint, a very important 

 fact that such natural mixtures consist in the main almost 

 always of components which belong to the same chemical 

 family. 



The natural oils and fats which are distributed throughout 

 the vegetable and animal kingdoms afford us numerous 

 instances of mixtures. 



EXAMPLES : {a) Arachis Oil (seed of Arachis hypogcea) 

 contains glycerides of stearic, arachidic, lignoceric, oleic, hypo- 

 gaeic, linolic acids, etc.^ 



(b) In Linseed Oil (seed of Linum usitatissimum) , the com- 

 position of which is not yet fully known, glycerides of palmitic, 

 arachidic, linolenic, oleic acids have already been discovered. ^ 



(c) In Cow Butter glycerides of the following acids occur : — 

 butyric, caproic, caprylic, capric, lauric, myristic, palmitic, 

 stearic, oleic. ^ 



Microscopical observation does not give us the slightest idea 

 of the complicate composition of the natural mixtures which 

 we call arachis oil, linseed oil and cow butter. 



It may be remarked that the same glyceride very often 

 occurs among the components of several oils and fats (for 

 instance, oleic acid is found in the three above examples 

 and many others ; arachis oil and linseed oil have two com- 

 ponents in common, although they are found in plants which 

 belong to different famihes). 



ANOTHER EXAMPLE: There are in opium (latex of 

 Papaver somniferum) neutral compounds, acids and some 

 twenty alkaloids, the most important of which is Morphine.^ 



1 THORPE, loc. cit., vol. 1.(1912), p. 286. ^ /jj^^ ^0!. iii. (1912), p. 324. 



^ Ibid., vol. i. (1912), p. 577. * Ibid., vol. iv. (1913), p. 19. 



