CHEMICAL COMPOSITION 63 



It has already been stated that the essential structures in 

 the bacterial cell are cell wall and protoplasm, including 

 the nuclein. These diflFer markedly in chemical composi- 

 tion. 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 ventriculi, Migula; Mycobacterium tuberculosis, Ham- 

 merschlag, Dreyfuss, Nishimura; Bacillus subtilis, Drey- 

 fuss; Acetobacfer xylinum, Brown; Acetobacter acidi oxalici, 

 Banning; and a few others.) It is certainly not an impor- 

 tant 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 associ- 

 ated with these substances are compounds containing nitro- 

 gen. One of these has been certainly identified as cJiitin or 

 a closely similar substance. Chitin is the nitrogenous sub- 

 stance which enters largely into the composition of the hard 

 parts 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 lio-ht 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. 



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

 CeHigOs not soluble in water, alcohol, ether or dilute acids but soluble in an 

 ammoniacal solution of copper oxide. It gives with iodine and ^Iphuric 

 acid a blue color and with iodine zinc chloride a violet and yields dextrose on 

 hydrolysis." — H. Fischer. 



