1. In view of the markedly short period of gestation in the dog and in view of the relatively large litters that are cast and nursed, this species when compared with the human being undergoes a much greater physiological strain during pregnancy and lactation. This is evidenced by marked decreases in the hematocrit values, in total cell volumes and in the serum protein concentrations, by an appreciable plasma hydration, and in some cases by significant reductions in the total circulating serum protein.

2. When pregnant dogs are fed a protein-free diet at a high level of caloric intake and are subjected to our standardized plasmapheresis technique, it is possible to deplete the animal of its reserve serum protein stores and reduce the serum protein concentration to the basal level (3.5 to 4.2 per cent) within the extremely short period of from 2 to 3 days. This indicates that the dog during pregnancy possesses a very limited amount of reserve serum protein.

3. Once the basal serum protein level is attained, the pregnant or lactating dog exhibits a marked impairment in its ability to regenerate serum protein. The synthesis of body proteins in the fetus during pregnancy and the milk proteins during lactation is considered to be actually an internal plasmapheresis, leading to a depletion of the serum protein by the preferential utilization of the materials from which this complex is made. These parasitic effects on the maternal organism are believed to be of primary importance, over and above any hydremia, in causing the lowered serum protein concentrations characteristic of pregnancy.

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