308 ANIMAL PHYSIOLOGY. 
and in man is viscid, while the secretion of the sublingual 
gland is still more viscid. 
Comparative——Saliva differs greatly in activity in different 
animals; thus saliva in the dog is almost inert, that of the 
parotid gland quite so; in the cat it is but little more effective ; 
and in the horse, ox, and sheep, it is known to be of very feeble 
digestive power. 
In man, the Guinea-pig, the rat, the hog, both parotid and 
submaxillary saliva are active; while in the rabbit the sub- 
maxillary saliva, the reverse of the preceding, is almost in- 
active, and the parotid secretion very powerful. 
An aqueous or glycerine extract of the salivary glands has 
digestive properties. The secretion of the different glands 
may be collected by passing tubes or cannulas into their ducts. 
Pathological. Potassium sulphocyanate (which gives a red 
color with salts of iron) is sometimes present normally, but is 
said to be in excess in certain diseases, as rheumatism. 
The saliva, normally neutral or only faintly acid, may be- 
come very much so in the intervals of digestion The rapid 
decay of the teeth occurring during and after pregnancy 
seems in certain cases to be referable in part to an abnormal 
condition of the saliva, and in part to the drain on the lime 
salts in the construction of the bones of the fcetus. 
The tartar which collects on the teeth consists largely of 
earthy phosphates. 
Gastric Juice—Gastric Juice may be obtained from a fistu- 
lous opening into the stomach. Such may be made artificially 
by an incision over the organ in the middle line, catching it up 
and stitching it to the edges of the wound, incising and insert- 
ing a special form of cannula, which may be closed or opened 
at will. 
Digestion in a few cases of accidental gastric fistulee has 
been made the subject of careful study. The most instructive 
case is that of Alexis St. Martin, a French Canadian, into 
whose stomach a considerable opening was made by a gunshot- 
wound. 
Gastric juice in his case and in the lower animals with arti- 
ficial openings in the stomach, has been obtained by irritating 
the mucous lining mechanically with a foreign body, as a feather. 
The great difficulty in all such cases arises from the impos- 
sibility of being certain that such fluid is normal; for the con- 
ditions which call forth secretion are certainly such as the 
stomach never experiences in the ordinary course of events, 
