Lowered plasma protein concentration following single injections of gum acacia in the dog is due in some part to dilution, and in greater part to actual decrease in total circulating protein. The maximum decrease in the total circulating protein does not take place at the same time as the maximum decrease in concentration. Fluctuations in fibrinogen concentration are marked, and are not necessarily proportional to changes in plasma protein concentration. Plasma protein concentration returns to normal limits within 10 to 21 days after the injection, at which time total circulating protein and plasma volume are lower than normal. Loss of protein cannot be accounted for by increase in urinary nitrogen. It is possible to maintain dogs at low levels of plasma protein concentration for several weeks by repeated injections of gum acacia solution. Anatomical changes following such a procedure in a normal dog are most conspicuous in the liver (Fig. A). These observations further implicate the liver as a source of plasma protein. Two mechanisms for the diminution of plasma protein following gum injection are suggested. One of these is based on the possibility that the liver cells being engorged with gum acacia are not able to produce the necessary amount of plasma protein to supply the normal demand. The other possibility is that with the injection of the gum, since there is obviously a greatly increased amount of colloid in the blood, the more readily removable colloid, i.e. plasma protein, is taken out of the blood stream, in an attempt to return plasma volume and colloid osmotic pressure to the normal limits. It is probable that both of these mechanisms are involved. Injection of gum acacia is suggested as a technique for further study of disturbed liver function. It must be obvious that clinical use of gum acacia for intravenous injection is not without danger.