DESCRIPTION OF FEEDING-STUFFS 177 



this food tends to flavour the milk and butter in an 

 objectionable way. 



2. Potatoes. Starch is the chief constituent of 

 the dry matter of potatoes, and it is this which 

 forms the bulk of the digested material. Crude pro- 

 tein and fat are only present in small quantities, 

 and 40% or so of the former is in the form of 

 non-protein nitrogenous substances. A poisonous 

 material " solanine " is a regular constituent of all 

 parts of the potato plant, the tubers containing 

 about -i gram in 1 kilogram. Although this poison 

 does not increase when the potatoes are stored, 

 or when they decompose, it passes in considerable 

 quantities into the young shoots when the tubers 

 germinate, so that the sprouts may contain as much 

 as 50 grams per kilogram. This means that the 

 young sprouts should not on any account be used 

 in feeding. Increase of the solanine to three times 

 the original amount was also noticed when the 

 potatoes were placed in the light and allowed to go 

 green on one side. Scabby potatoes do not, 

 however, contain more solanine than sound ones, 

 but it has been found that heavy dressings of 

 nitrogenous manures cause the amount of this 

 poison to increase. 



The composition of potatoes depends upon the 

 same conditions as it does in the case of mangels, etc. 

 After wet weather, liberal nitrogenous manuring, 

 early harvest, etc. the tubers are watery and poor 



