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This report describes fine structural changes of interphase nuclei of human peripheral blood lymphocytes stimulated to growth by short-term culture with phytohemagglutinin. Chromatin is found highly labile, its changes accompanying the sequential increases of RNA and DNA synthesis which are known to occur in lymphocyte cultures. In "resting" lymphocytes, abundant condensed ehromatin appears as a network of large and small aggregates. Early in the response to phytohemagglutinin, small aggregates disappear during increase of diffuse ehromatin regions. Small aggregates soon reappear, probably resulting from disaggregation of large masses of condensed chromatin. Loosened and highly dispersed forms then appear prior to the formation of prophase chromosomes. The loosened state is found by radioautography to be most active in DNA synthesis. Small nucleoli of resting lymphocytes have concentric agranular, fibrillar, and granular zones with small amounts of intranucleolar chromatin. Enlarging interphase nucleoli change chiefly (1) by increase in amount of intranucleolar chromatin and alteration of its state of aggregation and (2) by increase in granular components in close association with fibrillar components.

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When blood plasma proteins are depleted by bleeding with return of the washed red cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a constant level of plasma protein production if the diet protein intake is controlled and limited. Such dogs are outwardly normal but have a lowered resistance to infection and to certain intoxications. When the protein intake of such dogs is completely replaced by the growth mixture (Rose) of crystalline amino acids, plasma protein production is excellent, weight and nitrogen balance are maintained. This growth mixture consists of ten amino acids, threonine, valine, leucine, isoleucine, tryptophane, lysine, phenylalanine, methionine, histidine, arginine, and is as effective as most diet proteins in plasma protein production. The above amino acid mixture in aqueous solution may be given by vein with equally good plasma protein production and no apparent clinical disturbance even when given rapidly. Cystine may replace methionine in the above mixture with equally good plasma protein production for 7 to 10 days but at the expense of the body tissues, that is, with weight loss and a negative nitrogen balance. The addition of cystine to the protein-free, otherwise adequate diet may result in the production of considerable new plasma protein during a period as long as 1 week (cystine effect). This reaction may depend upon the amino acid constitution of the preceding diet protein in that it occurred following a liver feeding but did not occur after pancreas feeding. Arginine is required in the diet of the protein depleted dog for fabrication of plasma protein. It is apparently not needed for nitrogen balance for as long as 1 or 2 weeks. The omission of either threonine or valine from the growth mixture is quickly followed by a sharp decline in plasma protein formation and by a negative nitrogen balance. When histidine, arginine, and most of the lysine are omitted from the growth mixture, nitrogen balance and weight may be maintained for as long as 1 week but plasma protein production falls off markedly. The findings indicate that the growth mixture of amino acids should be a valuable addition to transfusion and infusion therapy in disease states associated with deficient nitrogen intake or tissue injury and accelerated nitrogen loss, including shock, burns, and major operative procedures.

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When blood plasma proteins are depleted by bleeding with return of the washed red blood cells (plasmapheresis) it is possible to bring dogs to a steady state of hypoproteinemia and a uniform plasma protein production on a basal low protein diet. These dogs are clinically normal. Introduction of variables into their standardized life gives insight into the production of plasma protein. Casein retested as the basal protein in the ration may show high yield of plasma protein, equal to 33 per cent of the protein fed. This equals the potency of liver protein (17 to 33 per cent) and approaches the utilization of plasma protein by mouth (40 per cent). Zein has no effect upon plasma protein regeneration but when it is supplemented with cystine, tryptophane, lysine, and glycine, there is a doubling of the liver basal plasma protein production and a retention of the fed protein nitrogen. Threonine does not modify the above reaction. Liver protein supplemented with cystine, leucine, glutamic acid, and glycine in the basal diet yields double the amount of new formed plasma protein compared with liver alone. This combination is then as potent as plasma protein itself when given by mouth—40 per cent utilization. Tyrosine or lysine, arginine, and isoleucine do not modify the above responses. Methionine is not as effective as cystine in supplementing gelatin and tyrosine to produce plasma protein. Cystine, leucine, and glutamic acid appear to be of primary importance in the building of new plasma protein in these experiments. Plasma protein formation is dependent upon materials coming from the body reserve and from the diet. Given an exhaustion of the reserve store there is very little plasma protein produced during a protein fast (3 to 6 gm. per week). A turpentine abscess does not modify this fasting plasma protein reaction. Homologous plasma given by vein will promptly correct experimental hypoproteinemia due to bleeding. It will maintain nitrogen equilibrium and replenish protein stores. Even during hypoproteinemia plasma protein may promptly pass out of the circulation to supply body needs for protein. Perhaps the most significant concept which derives from all these experiments is the fluidity of the body protein (including plasma protein)—a ready give and take between the protein depots—a "dynamic equilibrium" of body protein.