6 THE QUANTITATIVE METHOD IN BIOLOGY 



observed in a drop of milk by means of the most powerful 

 microscope, seems to be a homogeneous mass, although it con- 

 sists of nine different kinds of glycerides. It is therefore quite 

 conceivable that a chromosome, a centrosome, the living 

 stroma of a chloroplast, etc., contain a number of bioproteic 

 components. 



By the investigation of the differentiated parts of the living 

 substance we may acquire very valuable knowledge of numer- 

 ous observable properties and functions of the cells, yet we are 

 not enabled to probe to the actual bottom of the subject. A 

 biologist is sometimes induced to believe that it is possible, by 

 proceeding along this path of study, to attain the limits of our 

 science with regard to the explanation of the facts of heredity, 

 variation and origin of species. Feeling themselves deceived, 

 after many years of work, certain biologists seek for an explana- 

 tion in a so-caUed vital force, which is a matter of belief and not 

 susceptible of scientific analysis. 



We must always bear in mind that all the differentiations 

 and functions of the living substance, and also its physical 

 constitution, after all is said and done, depend on the way in 

 which the molecules of its components are built up. As soon 

 as we want to look further, we leave the field of exact science. 



§ 8.— BIOTIC AND ABIOTIC CHEMICAL PROPERTIES. 

 — A living mixture may include and probably always includes 

 substances which do not belong to its intrinsical components. 

 Such substances might be called abiotic ; they may be absorbed 

 from without {examples : food, oxygen and eventually any 

 substance for which the living mixture is permeable), or pro- 

 duced within the living mixture and used for various physio- 

 logical purposes (glucose and more respiratory combustibles), 

 or excreted (carbonic acid) or stored (starch, proteins in the form 

 of aleuron, etc.), etc. 



The abiotic substances which are included in the living 

 mixture (and also, of course, in the vacuolar liquid and the ceU- 

 walls) are exceedingly numerous, and many of them are 

 characteristic of certain species or groups of species. 



EXAMPLES : Morphine in Papaver, nicotine in Nicotiana, 

 dipsacine and dipsacotine in many Dipsacece ; colouring and 

 odorous substances in numerous plants and animals ; for 

 instance, in Phallus impudicus, Chara, Cicindela, Coccinella, 

 bugs, etc. 



The so-called chemical characteristics of a species, which 

 depend on the presence of abiotic substances, are to be strictly 

 distinguished from the biotic chemical properties of the specific 

 living mixture. This mixture is the laboratory in which the 

 alysarine of Rubia iinctorum, the coumarine of Asperula 



