THE CHEMISTRY OF THE TISSUES AND ORGANS. 
By W. 1). Halliburton. 
Contexts. — Cells and Protoplasm, p. 80 ; Liver, p. 85 ; Spleen, p. 87 ; Thymus, 
p. 88 ; Thyroid, p. 88 ; Suprarenals, p. 90 ; Pancreas, p. 92 ; Kidneys, p. 
92 ; Testis, p. 92 ; Muscle, p. 95 ; Skeletal Tissues, p. Ill ; Nervous Tissues, 
p. 115 ; The Eye, p. 121 ; Milk. p. 125. 
The preceding article contains an account of the principal proximate 
principles occurring in the body and in food. 
In the present article I propose to present the subject from another 
standpoint, and to discuss the chemical composition of the various 
animal tissues and organs. This will in great measure be complemental 
to what has been already done, and will give the opportunity of describ- 
ing some substances which have only been treated incidentally in the 
foregoing chapter. 
In describing the chemistry of the organs, I shall endeavour to avoid 
discussions as to their metabolic functions, and shall omit all considera- 
tion of their secretions, since these are treated elsewhere in this work ; 
an exception, however, will be made in the case of milk. 
Protoplasm and cells. — The chemical structure of living substance 
is still beyond our knowledge. All that chemists are able to do is to 
examine the disintegration products of the substance which the}" un- 
avoidably kill by the use of reagents. 
Some authors speak of living substance as if it wore merely proteid 
in composition, and have adopted the phrase " living proteid " (see p. 38). 
But it is doubtful if the use of such a term is justifiable, for proto- 
plasm even in its simplest condition invariably contains, or yields on 
disintegration, substances other than proteid, though proteids and 
compound proteids like nucleo-proteid are by far the most abundant of 
these disintegration products. Among the other solid substances con- 
stantly present in protoplasm are lecithin, cholesterin, and inorganic 
salts (especially phosphates and chlorides of calcium, sodimn, and 
potassium): and frequently fat and carbohydrate material, such as 
glycogen, are also to be found. Water occurs to the extent of 75 per 
cent, or more. "Whether these substances are all present in the free 
state, or, as is much more probable, are linked together in intimate 
union, to form the complex protoplasmic molecule, it is at present 
impossible to say with certainty. Living cells are alkaline ; after death 
they become acid. 
The simplest form of protoplasm known is that foimd in the 
Plasmodium of the myxomycetous fungus, Jfithalivm septicum. It has 
