ASSIMILATION. 201 



called proteine compounds. In their production from the crude 

 sap, the ammonia, or other azotized matter it contains, plays an 

 essential part ; and oxygen gas is restored to the air from the de- 

 composition of all the carbonic acid concerned and a part of the 

 water.* 



.355. Tn living cells the proteine exists as azotized mucilage, and 

 forms the protoplasm or vitally active lining which may be said to 

 give origin to the vegetable structure, since the cellulose is depos- 

 ited, under its influence to form the permanent walls or fabric of 

 the cells, as has already been explained (27-32). When the 

 cells have completed their growth and transformation, the proto- 

 plasm abandons them, being constantly attracted onwards into 

 forming and growing parts, where it incites new development. For 

 this azotized matter has the remarkable peculiarity of inducing 

 chemical changes in other organic products, especially the neutral 

 ternary bodies, causing one kind to be transformed into another, or 

 even the decomposition of a part into alcohol, acetic acid, and 

 finally into carbonic acid and water (as in germination, &c-), it- 

 self remaining the while essentially unaltered. 



356. The constant attraction of the protoplasm from the com- 

 pleted into the forming parts of the plant explains how it is, that 

 so small a percentage of azotized matter should be capable of 

 playing such an all-important part in the vegetable economy. It 

 does its work with little loss of material, and no portion of it is 

 fixed in the tissues. At least, the little that remains in old parts is 

 capable of being washed out, showing that it forms no integral part 

 of the fabric. It explains why the heart-wood of trees, especially 

 the most solidified kinds, yields barely a trace of nitrogen, while 

 the sap-wood yields an appreciable amount, arid the cambium-layer 



* The chemical changes have been tabulated thus: 



The materials: From which are formed the product: 

 C. H. N. O. C. H. N. O. 

 74 of Water, 74 74 1 of Proteine, 48 36 6 14 

 94 of Carbonic acid, 94 188 4 of Cellulose, 48 40 40 

 a of Carbonate of 21 2 of Oxygen lib- 

 ammonia, 226 4 crated, 212 



96 76 6 266 96 76 6 266 



It seems now lobe conceded, that proteine, as well as all its transformations 

 or states, contains also, as essential constituents, a minute quantity of sulphur 

 and phosphorus, one or both (10). 



