The introduction into the blood stream of dilute hydrochloric acid or sodium carbonate in quantities not too great to be compatible with life results in marked alterations in the color of certain of the matrix tissues stainable in vivo with phthalein indicators. Connective tissue in its various forms, and tendon and cartilage all become relatively more acid or alkaline than the normal. The hue of the kidney cortex also changes, as might be expected from its functions. The pancreas and lymph nodes, on the other hand, appear unaffected even when the injection is pushed to the extreme; and the slight to negligible alterations in the hue of the liver may be due to changes in the color of the associated secretion. The matrix tissues just mentioned behave as if unable to maintain a reaction of their own; whereas the elements of the parenchymal organs would seem to make their own conditions even when so much acid or alkali has been injected as will lead to death of the animal.

Injections of lactic acid are well tolerated and it is difficult to bring about alterations in the color of the phthalein-stained matrix tissues by means of them. Salt solution, and sugar in large amount cause no changes in color such as would indicate changes in reaction.

The results with the various phthalein indicators are in close accord, attesting that the information these give under vital conditions is reliable.

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