412 



OF FOOD, AND THE DIGESTIVE PROCESS. 



cular type of which an example has been already given from the glands of 

 Brunner ( 234); their ultimate follicles (Fig. 29) are very minute (their 

 average diameter being only about l-1200th of an inch), and are closely sur- 

 rounded by a plexus of capillary bloodvessels (Fig. 28). Their development 

 commences from a simple canal, sending off bud-like processes, which open 

 from the mouth, and lie amidst a cellular blastema; and as their evolution 

 advances, the large parent-cells of this blastema form communications with 

 the gland-canal, which is at the same time extending its ramifications, and re- 

 main as the terminal follicles of these. 



437. The inquiry into the chemical constitution and properties of the Saliva 

 has for the most part been limited to the fluid obtained from the mouth, rather 

 than to that secreted by the glands. The specific gravity of this fluid is usually 

 (according to Lehmann) from 1004 to 1006; but it may rise to 1008 or 1009, 

 or may sink to 1002, without any indication of co-existing disease. When ex- 

 amined microscopically, the Saliva is found to contain a small number of minute 

 corpuscles derived from the Salivary glands, and large epithelial scales thrown 

 off by the buccal mucous membrane. Its reaction is usually alkaline, that of 

 the Saliva furnished by the principal glands being always so (in the state of 

 health), whilst that of the buccal mucous membrane is acid; so that when the 

 former predominates, as is always the case when food is being masticated and 

 digested, the saliva of the mouth is alkaline ; whilst, when the latter is more 

 abundant, as is often the case during the intervals of digestion, from the slow 

 rate at which the salivary glandules then pour forth their product, the buccal 

 saliva is frequently acid. The following are two of the most recent analyses of 

 this fluid that have been made; the one by the eminent chemist Frerichs, 1 whose 

 contributions to the Physiology of Digestion are among the most valuable of the 

 results which have been furnished by recent inquiries in this direction ; and the 

 other by Dr. Wright, 9 who has made a special study of the Salivary secretion. 



Dr. Wright. 



Dr. Frerichs. 



Water 



Solid Matters 



Ptyalin . 



Mucus (and epithelium) 



Fatty matter 



Albumen (with soda) 



Sulphocyanide of potassium 



Alkaline and earthy salts 



Loss 



994.10 

 5.90 



1.41 



2.13 

 .07 

 .10 



2.19 



100.00 



The total proportion of solid matter, as the preceding analyses show, is subject 

 to great variation; it seems commonly to range between 7 and 12 parts in 1000; 

 but may even reach 16 parts. We shall presently see, however, that this varia- 

 tion may be partly attributed to a difference in the proportions of the fluid 

 poured into the mouth by the several glands which secrete it. The substance 

 to which the designation of Ptyalin is given is that on whose presence the pecu- 

 liar properties of the Saliva appear to depend; and it appears, as regards its 

 chemical nature, to be an albuminous compound, in such a state of change, how- 

 ever, that it acts the part of a " ferment." 3 The presence of sulpho-cyanogen 



1 See "Canstatt's Jahresbericht," 1850, p. 136; and "Wagner's Handwurterbuch," 

 art. "Verdauung." 



2 "Lancet," March, 1842. 



3 The following, according to Prof. Lehmann ("Lehrbuch der physiologischen Che- 

 mie," band ii.), are the distinctive chemical characters of ptyalin. Being held in solu- 



