GRASSES OF IOWA. 465 



protein is used to designate that part of the substance which 

 contains nitrogen and which may be called the nitrogenous 

 part. 



Albuminoids are those substances which form the most use- 

 ful parts of the protein substances. The protein substances 

 which are not albuminoids have the nature of substances 

 which are called amides. These amides are of much less 

 value for food purposes than the albuminoids. 



Crude fiber is the more or less indigestible or woody parts 

 of the food. 



Ash is that part of the food which remains after burning 

 and consists of the salts found in the food substances 



The action of the digestive system may be compared to a 

 process which is a combina ion of grinding, crushing and ex- 

 tracting substances in order to obtain the useful parts. 



The food is first taken into the mouth where the teeth grind 

 and crush it, breaking it into small pieces and mixing the 

 resulting mass with the saliva. The saliva is a substance 

 which is largely water but there is a peculiar ferment called 

 ptyalin. This ferment when it is mixed with any substance 

 containing starch commences to turn it to sugar. As an illus- 

 tration, in order to show its composition we may take the 

 analysis of the saliva of various domestic animals ; the results 

 being stated in parts per 1000 (*). 



HORSE. 



Water 992 00 



Mucus and albumin 2 00 



Alkaline carbonates 1.08 



Alkaline chlorides 4.92 



Alkaline phosphates and phosphates of lime trace 



Total 1000 00 



Cow. Sheep. 



Water 990.74 989.00 



Mucus and albumin 44 1.00 



Alkaline carbonates 3.38 3.00 



Alkaline chlorides 2.85 6.00 



Alkaline phosphates 2.49 100 



Phosphates of lime 10 trace 



Totals 1000.00 1000.00 



In the mucus and albumin present there occurs the ferment 

 called ptyalin. This ptyalin is always present in saliva, even 



• Smith, Physiology of Domestic Animals. 271. 



