The Chemical Constituents of the Organism. 11 



duction of entirely new substances. A common illustration 

 of ferment activity is the yeast-plant, which is capable of 

 producing out of sugar, alcohol and carbonic acid ; its func- 

 tion is due to a living cell, and such a ferment is described 

 as organized : micro-organisms, such as are found in the 

 intestinal canal and other places, which are capable of pro- 

 ducing great changes in the constitution of organic fluids, 

 are also classed as organized, for example, the lactic acid 

 ferment or bacillus, and the bacillus splitting up urea into 

 carbonate of ammonia, etc. In the body another class of 

 ferment exists, which, as it does not depend upon a living 

 cell, is described as unorganized or soluble ; such is the 

 •ferment which converts starch into sugar, the so-called 

 amylolytic ; the proteolytic or ferment converting proteids 

 into peptones; the fat-splitting ferment, which breaks up 

 fat into glycerin and fatty acids ; the milk- curdling ferment 

 of the fourth stomach of the calf ; the fibrin- forming fer- 

 ment of the blood, etc. : all these can by appropriate means 

 be isolated from the various tissues which produce them. 



Almost all dead tissues and organic fluids may act as 

 starch-converting ferments. 



Both the unorganized and organized ferments agree in so 

 far as their general action is concerned. All of them are 

 destroyed by raising the fluids containing them to a certain 

 temperature ; none of them appear to suffer, that is to be 

 worn out or exhausted, by the amount of work they per- 

 form, and in consequence in each case a small quantity of 

 them will produce as great an effect as a larger quantity. 



The Pigments of the body are classed as proteids ; com- 

 paratively little is known about them, though they are 

 widely distributed and perform important functions. The 

 best known animal pigment is hemoglobin, the red colouring- 

 matter of the blood ; it is of a proteid nature, yet crystalliz- 

 able, and it also contains iron ; it acts as an oxygen carrier, 

 and is often spoken of as a respiratory pigment ; it has 

 several derivatives (see Blood), which supply the colouring 

 matter of the bile, urine, and feces. The next pigment 

 widely distributed is the black pigment of the body, or 



