40 DIGESTION AND FOOD. 



interesting group of substances. If the proportions held to 

 other alimentary principles is considered sufficient to deter- 

 mine their relative value, we must class the hydro-carbons 

 first in the list, though much depends on the climate in 

 which animals live. Amongst us, the consumption of heat- 

 giving food is and must necessarily be enormous, and to the 

 horse, destined as he is for fast work, the supply of materials 

 for the rapid combustion which must incessantly go on in his 

 system must be very great. 



I. STARCH (Ci2 HI O OIQ) stands at the head of this group. 

 It was for long considered characteristic of plant structure, 

 but, within the last few years the researches of microscopic 

 anatomists have proved the existence of amyloid or starchy 

 bodies in the tissues of animals. 



Herbivorous quadrupeds are constantly receiving various 

 kinds of starch into their systems. The varieties are distin- 

 guished by a peculiar shape of the granule, as indicated by 

 the microscope. They all indicate the same chemical proper- 

 ties, being transformed into dextrine or British gum by the 

 action of saliva or malt. In both cases, a nitrogenous body 

 an animal diastase is regarded as inducing the change, 

 though this is brought about even by heating starch to a 

 certain point in sealed tubes, with water containing 1-5 00th 

 part of oxalic acid. The dextrine, which passes into the 

 intestines or which continues to be acted upon as above, is 

 further transformed into glucose or grape-sugar, in which 

 form the hydro-carbons are largely found in the blood of the 

 mesenteric veins of any of our domestic animals, and, strange 

 to say, in carnivora as well as herbivora. Starch is tested 

 by iodine, with which it forms a blue colour, supposed to be 

 owing to the iodine becoming finely divided, and adhering to 

 the starch as a dye does to the fibres of cloth. 



It is glucose that we find in the blood of animals, and 



