66 ELEMENTS OF BIOLOGY. 



Little need be said here as to the occurrence of the 

 so-called ''incidental elements." Sulphur occurs in albu- 

 men, as one of its constituents, and phosphorus is found in 

 nervous matter, and is largely present in bone (as phosphate 

 of lime). Chlorine occurs (as chloride of sodium) in ani- 

 mal juices, and in gastric juice (as hydrochloric acid). 

 Fluorine (in the form of fluoride of calcium) occurs in the 

 teeth. Silicon, aluminium, calcium, and magnesium, occur 

 in the teeth and bones. Sodium and potassium are found 

 in the blood, and the former is chemically combined with 

 albumen in its soluble state. Iron is found in the colouring- 

 matter of the blood, and, unlike the other metals, is pro- 

 bably present in an uncombined condition. Manganese 

 has been detected in hair, and is also stated to occur in the 

 blood. Lastly, copper is found in the liver and in bile, and 

 in some colouring-matters. 



The " essential " elements, carbon, hydrogen, oxygen, and 

 nitrogen, occur united with compounds, which, " from their 

 being supposed to stand, in order of simplicity, nearest to 

 the elements," are called proxijfiate prmciples. In other 

 words, these four elements form a series of compounds 

 which have a definite chemical composition, which may be 

 obtained in an isolated condition from animal and vegetable 

 bodies after death, and which in some cases can be artifi- 

 cially built up out of inorganic materials in the laboratory 

 of the chemist. The " proximate compounds " of both ani- 

 mals and plants may be divided into two groups, termed 

 non-nifrogenotis and nitrogenous, according as they consist of 

 carbon, hydrogen, and oxygen alone, or contain nitrogen in 

 addition to these three elements. 



The no7i-7iitrogenous compounds of animals are the various 

 Fats. These consist of carbon, hydrogen, and oxygen, 

 cornbined in such proportions that the oxygen would be 

 insufficient to form water with the hydrogen or carbonic 

 acid with the carbon. The exact functiors of the fats in 

 the animal economy cannot be said to have been as yet de- 



