72 CHEMICAL ENVIRONMENT 



the nuclein. These differ markedly in chemical corqposition. 

 It is well known that the cell walls of green plants consist 

 largely of cellulose and closely related substances.^ True 

 cellulose has been recognized in but very few bacteria. 

 (Sarcina ventricuU, Migula; Bacterium tuberculosis, Ham- 

 merschlag, Dreyfuss, Nishimura; Bacillus subtilis, Drey- 

 fuss; Bacterium xylinum, Brown; Bacterium acidi oxalici, 

 Banning and a few others.) It is certainly not an important 

 constituent of the cell wall in many. On the other hand, 

 hemicellulose and gum-like substances have been identified 

 in numerous organisms of this class as important constit- 

 uents of the cell wall and of the capsule which is probably 

 an outgrowth from the latter. Practically always associated 

 with these substances are compounds containing nitrogen. 

 One of these has been certainly identified as chitin or a 

 closely similar substance. Chitin is the nitrogenous sub- 

 stance which enters largely into the composition of the hard 

 part of insects, spiders and crustaceans. It is an interesting 

 fact to find this substance characteristic of these animals in 

 bacteria, as well as other fungi. 



Though it is extremely difficult to separate the cell wall 

 of bacteria from the cell contents, in the light of our present 

 knowledge it can be stated that the cell walls are composed 

 of a carbohydrate body closely related to cellulose, though 

 not true cellulose, probably in close combination with 

 chitin. 



Of the organic constituents of the cell contents the most 

 abundant are various proteins which ordinarily make up 

 about one-half of the dry weight of the entire cell. The 

 " Mycoproteid" of Nencki, 1879, and other earlier workers 

 is deserving of little more than historical interest, since these 

 substances were certainly very impure and probably con- 

 sisted of mixtures of several "proteins" in the more recent 

 sense. 



' "By cellulose is understood a carbohydrate of the general formula 

 (CoHioOs) not soluble in water, alcohol, ether, or dilute acids but soluble 

 in an ammoniacal solution of copper oxide. It gives with iodine and sul- 

 phuric acid a blue color and with iodine zinc chloride a violet and yields 

 dextrose on hydrolysis." — H. Fischer. 



