MODERN DEVELOPMENTS OF HARVEY'S WORK. 475 



of tlie utmost importance, and this is the admixture of blood from vari- 

 ous parts of the body. After describing the intestinal veins, Harvey 

 says: "The blood returning by these veins and bringing the cruder 

 juices along with it on the one hand from the stomach, where they are 

 thin, watery, and not yet perfectly chylified; on the other, thick and 

 more earthy, as derived from the fteces, but all pouring into this splenic 

 branch, ai-e duly tempered by the admixture of contraries," ' 



Harvey's chemical expressions are crude, for chemistry as a science 

 only began to exist about a century and a half after Harvey's death, 

 yet the general idea which he expresses in the words which I have just 

 quoted is wonderfully near the truth. 



Two of the most important constituents of the blood are chloride of 

 sodium nnd water. Chloride of sodium is a neutral salt, but during 

 digestion both it and water are decomposed in the gastric glands, and 

 hydrochloric acid is poured into the stomach, while a corresponding 

 amount of soda is returned into the blood, whose alkalinity increases 

 pan passu with the acidity of the stomach. Part of this alkali is 

 excreted in the urine, so that the urine during digestion is often neu- 

 tral or alkaline. Possibly some of it passes out through the liver in 

 the bile, through the pancreas and intestinal glands into the intestine, 

 where, again mixing with the acid chyle from the stomach, neutraliza- 

 tion takes place, so that neutral and comparatively inactive chloride of 

 sodium is again formed from the union of active alkali and acid. But 

 it is most probable that what occurs in the stomach occurs also in the 

 other glands, and that it is not merely excess of alkali resulting from 

 gastric digestion which is poured out by the liver, pancreas, and intes- 

 tine, but that these glands also decompose salts, pour the alkali out 

 through the ducts, and return the acid into the blood. 



We are now leaving the region of definite fact and passing into that 

 of fancy, but the fancies are not entirely baseless, and may show in 

 what directions we may search out and study the secrets of nature by 

 way of exi)eriment. For what is apparently certain in regard to the 

 decomposition of chloride of sodium in the stomach, and probably in 

 the case of neutral salts in the pancreas and intestine, is also probable 

 in that important though as yet very imperfectly known class of bodies 

 which are known as zymogens. Just as we have in the stomach an 

 inactive salt, so we have also an inactive pepsinogen, which, like the 

 salt, is split up in the gastric glands, and active pepsin is poured into 

 the stomach. But is the pepsin the only active substance prod need f 

 Has no other body, resulting from decomposition of the pepsinogen, 

 been poured into tlie blood while the i)ei)sin passed into the stomach? 

 Has the inactive pepsinogen not been split up into two bodies, active 

 when apart, inactive when combined? May it not be fltly compared, 

 as I have said elsewhere, to a cup or glass, harmless while whole, but 



' The Works of Wilham Harvey, Sydeuliam Society's eilitiou, page 75. 



