24 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



the existence of certain groupings of the atoms. Influenced in part by the 

 power of living material to reduce alkaline silver solutions, he supposes that 

 the specially important labile group in the molecule is the aldehyde radical 



_ O 

 C ~ TT . The nitrogen exists also in a labile amido- combination, NH 2 , 



and the active or living form of these two groups may be expressed by the 



-CH-NH 2 



formula I _Q. If this grouping by chemical change became con- 



-H 



verted to the grouping _ _ nT > ^ would form a comparatively inert 



compound such as we have in dead proteid. Starting with formic aldehyde 

 Loew and Bokorny give a schema according to which there might be con- 

 structed a living molecule containing the requisite aldehyde and amido- 

 groups ; thus : 



4HCOH + H 3 N - C 4 H 7 NO 2 + 2H 2 O. 



Formic Ammonia. Aspartic 

 aldehyde. aldehyde. 



Further possible condensation of the aspartic aldehyde would give 

 3(C 4 H 7 NO 2 ) ---- C 12 H 17 N 3 O 4 + 2H 2 O, 



and by still further condensation with the addition of sulphur and some re- 

 duction we would get 



6(C 12 H 17 N 3 4 )+12H + H 2 S == C 72 H 112 N 18 SO 22 + 2H 2 O, 



which represents, from their standpoint, the simplest expression of the struc- 

 ture of a proteid molecule possessing great lability and the power of further 

 polymerization. Latham l proposes a theory which combines the ideas of 

 Pfliiger and of Loew. He suggests that the living molecule may be composed 

 of a chain of cyan-alcohols united to a benzene nucleus. The cyan-alcohols are 

 obtained by the union of an aldehyde with hydrocyanic acid ; they contain, 

 therefore, the labile-aldehyde grouping as well as the cyanogen nucleus to 

 which Pfliiger attributes such importance. 



It has been assumed by many observers that the properties of living 

 matter, as we recognize them, are not solely an outcome of the inner structure 

 of the hypothetical living molecules. They believe that these latter units are 

 fashioned into larger secondary units each of which is a definite aggregate of 

 chemical molecules and possesses certain properties or reactions that depend 

 upon the mode of arrangement. The idea is similar to that advanced by 

 mineralogists to explain the structure of crystals. They suppose that the 

 chemical molecules are arranged in larger or smaller groups to which the 

 name "physical molecules" has been given. So in living protoplasm it may 

 be that the smallest particles capable of exhibiting the essential properties 

 of life are groups of ultimate molecules, in the chemical sense, having a 

 definite arrangement and definite physical properties. These secondary units 

 1 British Medical Journal, 1886, p. 629. 



