THE PHAGOCYTOSIS OF SOLID PARTICLES. 

 I. Quartz. 



By WALLACE O. FENN. 

 {From the Laboratory of Applied Physiology , Harvard Medical School, Boston.) 



(Received for publication, January 15, 1921.) 

 Measurement of Phagocytosis. 



The usual procedure for measuring phagocytosis is to incubate 

 suspensions of leucocytes and solid particles or bacteria together in 

 a test-tube for a given length of time; then to remove a sample and 

 make a smear of the mixture on a slide which is stained, mounted, 

 and counted at leisure. When bacteria are used as objects for 

 ingestion, as in opsonic index determinations, the actual number of 

 bacteria inside a given number of leucocytes is counted and com- 

 parisons are made on the basis of the average number of bacteria 

 taken up per leucocyte per unit of time. It is impossible to do this 

 with soHd particles which are usually larger than bacteria and hence 

 may almost completely fill the cell in a short time or become easily 

 superimposed. 



For this reason Hamburger (1), the author of the only extensive 

 quantitative experiments on phagocytosis of solid particles, always 

 counted the per cent of leucocytes containing solid particles per unit 

 of time. On theoretical grounds this method possesses the objection 

 pointed out by McKendrick (2) that it is not a measure of the amount 

 of work done but a measure of the number of cells which have done 

 the work. He shows, however, that if a normal frequency curve for 

 the distribution of the bacteria in the leucocytes is assumed, the 

 number of bacteria per leucocyte, i.e. the amount of work done, can 

 be calculated from the per cent of empty leucocytes, the former being 

 a logarithmic function of the latter, and he suggests that the deter- 

 mination of opsonic index may be simpHfied by counting only the 

 empty leucocytes. 



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