P revious Observations. The earliest observations on variations in percentage of salts in saliva with which we are acquainted, are those of Ludwig and B echer,* in 1851. They analysed successive portions of saliva, obtained under different conditions, from the submaxillary gland of the Dog. Three experiments were made on the effect of protracted secretion ; in two of these the percentage of salts sank in the successive portions of saliva, but in the remaining one, the third and fourth samples

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... saliva contained a rather higher percentage of salts than the second and first samples. The total amount of saliva collected in this case was 48*5 grm. Three experiments were made in the following m anner:-Saliva was collected, then blood withdrawn from the animal, water injected in the place of the blood, and saliva again collected ; in two of these experiments the defibrinated blood was re-injected, and a further portion of saliva obtained. In all these cases the percentage of salts in the saliva sank during secretion. Lastly, in one experiment fourteen samples of saliva were obtained, in all 177 grm .; and twice during the course of the experiment 150 grm. of a 7'33 per cent, solution of sodium chloride were injected. After the first injection there was a rise in the percentage of salts in the saliva ; after the second injection there was a fall in the percentage of salts below th at of the first sample. A few only of the samples of saliva were analysed. These observations showed th at during secretion the percentage of salts falls in most, but not in all, cases; and they indicated that the percentage of salts depends upon the condition of the gland with regard to fatigue. H eidenhain t placed the m atter on a different basis. He analysed successive small quantities of saliva, secreted at different rates, and found that, up to a certain limit, * Ludwig and at the percentage of salts in saliva does not always increase with an increase in the rate of secretion. But the only analyses given were of parotid saliva in the Dog, obtained first by stim ulating the sympathetic, and then by injecting pilocarpin. For an account of the recent observations of Novi, cf. p. 150. Unless otherwise mentioned the following 'procedure teas adopted in each of the Experiments. Morphia in 5 per cent, solution was injected sub-cutaneously; in half to three-quarters of an hour, when severe pinching of the skin produced no movement, the animal was given chloroform. A threeway tube was tied in the trachea, one limb of the tube being connected at intervals with a bottle con taining a m ixture of chloroform and ether. The lingual nerve was ligatured and cut peripherally of the point where it gives off the chorda ty m p an i; lifting this up, the central end of the lingual nerve and then the chordo-lingual were isolated