THE SALIVA. 143 



which this action is manifested, varies very much, as formerly noticed 

 by Lehmann, at different times ; and it is frequently impossible, even 

 with the mixture kept steadily at the temperature of 38, to find any 

 evidence of sugar under five, ten, or fifteen minutes. This difference 

 depends probably upon the varying constitution of the saliva itself. 



Notwithstanding the rapidity with which glucose begins to show itself 

 in a mixture of saliva with boiled starch, this action is not a very ener- 

 getic one ; that is, only a very small quantity of the starch is converted 

 into glucose within a given time, the greater portion remaining un- 

 changed. This is proved by the fact that such a mixture will show 

 the characteristic reaction of starch with iodine long after Fehlmg'a 

 test has shown the existence of traces of glucose. If a weak solu- 

 tion of boiled starch, made in the proportion of 3 parts of starch to 

 100 parts of water, be mixed with one-third of its volume of fresh human 

 saliva and placed in the water-bath at the temperature of 38, it will 

 often give, in one minute, a prompt sugar -reaction with Fehling's test ; 

 but it also contains, at the same time, an abundance of unaltered starch. 

 Even at the end of an hour, according to our own observations, the starch 

 is far from being entirely converted, as the mixture will still give a strong 

 purple-blue color on the addition of iodine. The same persistence of 

 starch in considerable proportion may be seen when the mixture is 

 retained in the mouth itself. If a thin paste of hydrated starch, con- 

 taining no traces of sugar, be taken into the mouth and thoroughly 

 mixed with the buccal secretions, it will often, as above mentioned, 

 begin to show the reaction of glucose in half a minute ; but some of the 

 starchy matter still remains, and will continue to manifest its character- 

 istic reaction with iodine for fifteen or twenty minutes, or even for half 

 an hour. 



The secretions produced by the different salivary glands vary some- 

 what in their physical properties, especially in the degree of their vis- 

 cidity, depending mainly upon the quantity of mucosine present. The 

 parotid saliva is obtained in a state of purity from the dog by exposing 

 the duct of Steno where it crosses the masseter muscle, and introducing 

 into it, through an artificial opening, a silver canula. The secretion 

 then runs directly from its external orifice, without being mixed with 

 that of the other salivary glands. It is clear, limpid, and watery, and 

 without the slightest viscidity. The submaxillary saliva is obtained in 

 a similar manner, by inserting a canula into Wharton's duct. It dif- 

 fers from the parotid secretion, so far as its physical properties are 

 concerned, chiefly in possessing a well marked viscidity. The sublingual 

 saliva is also colorless and transparent, and possesses a greater degree of 

 viscidity than that from the submaxillary. The secretion of the muci- 

 parous glandules, which forms properly a part of the saliva, is obtained 

 b}^ placing a ligature simultaneously on Wharton's and Steno's ducts, 

 and on that of the sublingual gland, so as to shut out from the mouth 

 all the glandular salivary secretions, and then collecting the fluid se- 

 creted by the buccal mucous membrane. This fluid is very scanty, and 



