The Chemical Constituent 's of the Organism. 3 



is taken up by the vegetable, and forming a part of the 

 proteid molecule is taken into the body of the animal, 

 where, by splitting up and oxidation, it yields sulphuric 

 acid, in which form it is excreted by the urine. 



Phosphorus enters plants as phosphoric acid united with 

 alkalies ; in soils it exists in only small quantities, hence the 

 necessity of phosphates as manure. In the plant phosphoric 

 acid forms a part of the complicated compounds known as 

 lecithin and nuclein, in which condition it enters the animal 

 body, forming a part of both the solid and fluid tissues. 



Chlorine does not exist in a free state in nature but com- 

 bined with potassium and sodium, in which form it enters 

 plants and from these passes in the same compounds into 

 animals. 



Neither sodium, potassium, nor magnesium enter or leave 

 the body or plant in any organic form, but simply as in- 

 organic salts. Bunge considers that calcium may enter the 

 body as an organic compound, his reasons for this view are 

 mentioned later in this chapter. 



Iron occurs free and in a ferrous and ferric state in nature ; 

 in the soil it permits the retention of carbon, and also 

 enables it to return to the atmosphere. 1 n the animal it is 

 an oxygen-carrier, combined with a highly complex body 

 known as haemoglobin. It furnishes the vegetable with its 

 colouring matter, for chlorophyll cannot be formed without 

 it. It is not known in what form iron leaves the body. 



Silicon, in the form of silicic acid, is taken up by plants, 

 through the aid of which the stems, which largely consist of 

 it, are capable of standing erect. Through the plant it is 

 taken into the body and passes into the tissues. It is largely 

 •of use in the development of hair, and much of it passes out 

 of the bodies of herbivora through the urine ; in sheep, ac- 

 cording to Bunge, it sometimes causes stone in the bladder. 



Bunge, in his remarkably clear style, having thus traced 

 the cycle of the elments from nature into the plant, from 

 the plant into the animal, and from the animal back to 

 nature again, then draws a contrast in the following terms 

 between the changes occurring in the animal and vegetable : 



1—2 



