ORIGIN OF PHAGOCYTIC MONONUCLEAR CELLS ah 
Since publication of the first report it has been found that 
even 40 mg. sodium citrate per cubic centimeter of blood does 
not prevent the ingestion of large numbers of staphylococcus 
pyogenes aureus when this organism in suspension is substituted 
for the lampblack. By using strengths of citrate varying 
between 5 and 15 mg. and substituting tubercle bacilli for the 
lampblack, 2.2 per cent is the maximum number of macro- 
phages containing the bacilli, while as many as 20 per cent of 
neutrophiles have ingested the organisms. In a small number 
of experiments with bacteria the limitation of phagocytosis to 
the mononuclear cells has not been successful. Leucocytes 
(polymorphonuclears and mononuclears) ingest the carbon in a 
plasma-free medium, provided the carbon has previously been 
brought into contact with fresh plasma or serum, although it has 
subsequently been washed (four times) with saline. Washed 
leucocytes, however, do not ingest untreated carbon. 
In preliminary experiments heavy suspensions of lampblack in 
1 per cent gelatin were injected intravenously into rabbits and 
dogs with discouraging results so far as the blood is concerned, 
for although polymorphonuclear leucocytes contained the carbon 
in abundance, very rarely could a mononuclear leucocyte be 
found which had ingested it. Only after repeated injections of 
large amounts did any mononuclear carbon-containing leuco- 
cytes appear in the peripheral blood of dogs. 
The next step was to inhibit by the simultaneous ‘njection of 
citrate the phagocytic activity of the polymorphonuclear leuco- 
cytes just as it had been successfully done in the test-tube. The 
amount of citrate to be injected was determined by estimating 
the weight of blood at one-twentieth of the body weight and 
injecting 7.7 mg. citrate per cubic centimeter of calculated 
blood. 
The exact way in which the citrate acts in the blood stream to 
prevent phagocytosis is problematical, but there are indications 
that it acts by diminishing the protective colloid action of the 
albumin of the plasma and in this way allows flocculation of the 
carbon so that it may be ingested by the leucocytes. 
