286 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



5. The Quantity of Saliva. — As regards the total quantity of saliva 

 and the amounts contributed by the different glands, certain data may 

 be determined in all domestic animals by means of oesophageal fistulae. 

 To accomplish this, the food is first 'weighed, then the time of mastica- 

 tion determined, and finally the food is weighed again as it escapes from' 

 an oesophageal fistula. By subtracting the weight of the food when 

 given from the weight as it is collected from the oesophagus, the amount 

 of fluid added may be determined. In this way Colin found that a 

 small horse secreted five thousand grammes of saliva in an hour, a 

 medium-sized horse five thousand two hundred grammes, and a large 

 horse in the same time eight thousand eight hundred grammes ; from 

 which it may be concluded that a horse feeding on hay secretes from five 

 thousand to six thousand grammes of saliva per hour. If oats are given 

 as food, the amount of saliva poured out is one-third less than the above; 

 only one-half as much is secreted when green fodder constitutes the food, 

 and only one-third as much when roots, such as beets or turnips, are 

 given. Further experiments have shown that dried fodder absorbs four 

 times its weight of saliva, oats a little more than their own weight, meal 

 twice its own weight, and green fodders half their own weight. Hence, 

 the amount of the salivary secretion varies with the amount of moisture 

 contained in the food. It is believed that after twenty-four hours' fasting 

 the salivation is more active at the commencement of the meal than when 

 hunger commences to be satisfied. The reverse, however, is the case for 

 the parotids, as they do not at once reach their maximum activity after 

 a long fast. The above statement, however, seems to hold for the sub- 

 maxillaries, as they are never completely inactive. But as the parotids 

 secrete the greatest volume of fluid, the food first swallowed is drier, and 

 therefore swallowed with more difficulty than later when the parotids 

 have acquired their maximum activity. Then the quantity of secretion 

 decreases with the activity of mastication. 



The quantity of saliva poured out in twenty-four hours may be 

 estimated by means of the preceding data. Tor if hay absorbs more 

 than four times its weight of saliva, and the horse swallows one hundred 

 grammes of saliva each hour during fasting, it is easy to estimate the 

 total amount secreted. A horse which consumes five thousand grammes 

 of hay and five thousand grammes of dry fodder will require forty 

 thousand grammes of saliva for the deglutition of its food, to which 

 must be added about two thousand grammes for the eighteen hours of 

 abstinence, making in all forty-two thousand grammes, or eighty-four 

 pounds. In the ruminant the total amount of saliva secreted in twenty- 

 four hours is much larger. If we assume that an ox takes three hours 

 in a day to feed and five hours to ruminate, it is found that in six' or 

 eight hours forty thousand grammes of saliva are secreted ,. and during 



