30 STUDIES IN IMMUNITY. 



used to study the effect of a variation in leucocytes on the bacteri- 

 cidal property of the blood. This method consists in artificially 

 lowering the number of leucocytes in the circulating blood and 

 testing the bactericidal property of the blood before and after. 



The most efficient method of lowering the number of leucocytes 

 is to inject bacteria, but the method could not be used in this work, 

 as the introduction of bacterial substances might affect the bacteri- 

 cidal property of the blood in some manner. Instead of bacteria, 

 then, an emulsion of some fine inert powder such as carmin must be 

 used. It has been asserted that cooling an animal in water brings 

 about a fall in the number of leucocytes, but we have had no success 

 with this method. The injection of carmin generally produces a 

 rapid hypoleucocytosis. In certain cases, however, the fall in 

 white corpuscles does not follow. It is probable that the taking 

 up of grains of carmin by phagocytes depends on the tactile 

 reaction of these cells. It is important to determine that the 

 fluid in which the carmin is suspended has no positive chemio- 

 tactic influence on leucocytes, as shown by an experiment with 

 capillary tubes. 



EXPERIMENT 7. A guinea-pig weighing 355 grams had been 

 vaccinated against the vibrio of Massaouah. A small amount of 

 blood was taken from the animal and found to contain 11,000 

 leucocytes. One-tenth of a cubic centimeter of a rather thick 

 emulsion of carmin in salt solution (50 centigrams of carmin to 10 

 c.c. of fluid) was slowly injected into the jugular vein. Two hours 

 later the leucocyte count had fallen to 3000. Another small 

 amount of blood was taken. One cubic centimeter of serum from 

 each blood specimen was then placed in a tube and inoculated 

 with a 24-hour culture of Massaouah (1 loop of a culture suspended 

 in 10 c.c. of normal salt solution). 



NUMBER OF COLONIES. 



