So Journal of Agriculture. [8 Feb., 1907. 



THE ELEMENTS OF ANIMAL PHYSIOLOGY. 



W . A. Osborne, M.B., D.Sc, Professor of Physiology and Histology, 

 Dean of tl/e Faculty of Agriculture in the University of Melbourne. 



{Continued from page 72 g, Vol. iv.) 



CHAPTER IV. 



The Elements of Bio-Cheniistry. 



Of the many elements known to the chemist — some 77 in number — 

 only twelve are essential for the maintenance of animal life. These are 

 carbon, hydrogen, nitrogen, oxygen, chlorine, sulphur, phosphorus, sodium, 

 potassium, iron, magnesium, and calcium.* All these elements are found 

 in sea water or in soil, but the highly complex compounds which they form 

 in bioplasm, and which are essential to life, are never found in nature 

 except as products of life. Doubtless the chemist will one day be able to 

 build up these complex and highly unstable bodies from their elements, but 

 then only in successive stages, at considerable cost, and by the exercise of a 

 highlv-trained intelligence. Some of the sirnpler bodies, such as certain 

 sugars, have been so built up, but the process is both tedious and costly. 

 The chemical powers of living things are well exemplified in the case of 

 nitrogen compounds. Nitrogen occurs free in the air, making up about 

 four-fifths of its volume, but nitrogen compounds, produced apart from 

 life, are present in air, earth, and water only in extremely small amounts. 

 In every thunderstorm a small quantity of oxides of nitrogen is produced, 

 but such oxides never occur in bioplasm. It is with carbon and hydrogen 

 that the cell prefers nitrogen to be linked, and w^hen we find such bodies 

 anv where on the earth, such as ammonia or sal -ammoniac, we may be sure 

 that living things have been the cause of their formation. Plants have the 

 power of taking up oxides of nitrogen by their roots and of changing the 

 liature of the compound in their active cells, but such, a source of com- 

 bined nitrogen would never suffice for the needs of the many plants that 

 grow on the earth's surface or in the sea. It is to certain bacteria that we 

 must look for the performance of that most necessary task — the " fixing " 

 of nitrogen ; that is, the picking up of free nitrogen from the air and the 

 formation from it of such compounds as can readily be used by plants. 

 These nitrogen compounds are unstable bodies, so that if all life were 

 destroyed on the earth, the combined nitrogen would tend in the course of 

 time to become free. 



The carbon which is found in bioplasm in the form of complex com- 

 pounds was originally derived from the carbon dioxide which exists in the 

 atmosphere to the extent of only some three and a half parts per ten thou- 

 sand. If all life were to cease, these carbon compounds would rapidly 

 break down and revert to the condition of carbon dioxide. As it is, this 

 tendency is constantly in operation. How and where is it, then, that these 

 complex carbon compounds have been built up so that life may be possible? 

 For answer we must look to the vegetable kingdom, and particularly to 



*To this list might be added iodine, which occurs in the thyroid gland, and 

 fluorine, which is found in bone and tooth. The small quantities of silicon present 

 in the animal body mav be looked upon as an unavoidable, but harmless, impurity. 



