574 A MANUAL OF VETERINARY PHYSIOLOGY 



season and the nature of the food. In summer the loss by sweat 

 in working horses, and the extra transpiration by the air-passages, 

 all have to be made good. Animals receiving dry food require 

 more water than those on green herbage. According to Colin 's 

 researches, 4 kilogrammes (8-8 pounds) of hay require 16 kilo- 

 grammes (35 -2 pounds) of saliva, and the fluid for this has to be 

 drawn from the blood. When ' roots ' form a portion of the daily 

 diet the amount of water consumed becomes considerably reduced. 

 So much is this the case that sheep fed on roots and succulent 

 food are not watered ; and the rabbit receiving succulent food 

 does not drink. The assumption that neither of these animals 

 requires water is at once disproved by placing them on a diet of 

 dry food. Purging, haemorrhage, and diabetes, prove severe 

 sources of water-loss to the tissues. 



Thirst is badly borne by animals, certainly by the herbivora. 

 The capacity for work with horses falls off considerably, and as 

 the fluid contents of the digestive canal and tissues is drawn upon 

 the abdominal wall contracts, and the animal wears a pinched and 

 anxious look. Under these conditions in war, horses have been 

 known, on obtaining access to water, to drink until they died, 

 presumably from rupture of the intestines. 



The ordinary exhibition of thirst in stabled animals is at once 

 recognised by the trained eye. The horse that pricks his ears and 

 gazes intently when he hears the sound of a bucket, and the 

 peculiar motions of the mouth of the thirsty horse at the sight 

 of water, are indications as unmistakable as speech. 



Deprivation of fluid is productive of intense suffering. Hunger 

 may be taken philosophically, but not thirst ; one extinguishes 

 life in a few days, the other in a few weeks. So essential, indeed, 

 is the regular renewal of fluid that the sick animal, though turning 

 from food with disgust, never fails, but in one disease, to consume 

 fluid ; during the existence of acute abdominal pain a horse 

 will not drink, yet the leathery dryness of the mouth suggests 

 intense thirst. 



