24 AN AMERICA X 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 



— C ~ it • 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 Q. 11 this grouping by chemical change became con- 



= c -c j, 



f 1TT VII 



verted to the grouping __ ^ — PHOH' li wou ^ ^ orm a comparatively inert 



compound such as we have in dead proteid. Latham 1 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 ben- 

 zene 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. 



Actual investigation of the chemical structure of living matter can hardly 

 be said to have made a beginning. The first step in this direction has been 

 made in the study of the chemical structure of the group of proteids which 

 have usually been considered as forming the most characteristic constituent 

 of protoplasm. Proteids as we obtain them from the dead tissues and liquids 

 of the body have proved to be very varied in properties and structure, so 

 much so in fact that it is impossible to give a satisfactory definition of the 

 group. Man) of them can be obtained in a pure, even in a crystalline form, 

 and their percentage composition can therefore be determined with ease. 

 But the fundamental chemical structure that may be supposed to characterize 

 the proteid group, and the changes in this structure producing the different 

 varieties of proteids are matters as yet undetermined. Several promising 

 efforts have been made to construct proteids synthetically, but the results 

 obtained are at present incomplete. On the other hand, Kossel 2 has isolated 

 from the spermatozoa of certain fishes a comparatively simple nitrogenous 

 body of basic properties (protamine), which he regards as the simplest form 

 of pndeid and the essential cure or nucleus characterizing the structure of the 

 whole group. It is an interesting thought that in the heads of the sperma- 

 tozoa with their complex possibilities of development and hereditary trans- 

 mission, dependent as these properties must be upon the chemical structure 

 of the germ protoplasm, there may be found the simplest form of proteid. 

 Kossel's work, it may be noted, has not gone so far as to indicate the possible 

 molecular structure of the protamines. 



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 



1 British Medical Journal, 1886, p. 629. 

 Zeitschrift fur physiol. Chem., 1898; xxv. L899, xxvi. 



