PHAGOCYTOSIS 2Q7 



cocci, they collect round the cell, though they are not actually 

 ingested, and this is confirmed by Sellards. Killed leucocytes 

 probably undergo a sort of coagulation equivalent to rigor mortis, 

 which would prevent the ingress of bacteria. 



Sellards has shown that salts are as necessary for phagocytosis 

 as for agglutination. The isotonic solution in which the 

 leucocytes were suspended was 5*5 per cent, of saccharose; the 

 bacteria were opsonized by fresh serum, washed thoroughly, and 

 suspended in the same sugar solution. Little or no phagocytosis 

 occurred, but it took place if salts were added. This, again, does 

 not look like a vital process, but is quite analogous with agglutina- 

 tion, in which we have every reason to believe that the effect is 

 due to an alteration of surface tension. So also with the action of 

 serum in aiding the phagocytosis of substances such as carmine or 

 carbon. We have only to suppose that some substance is occluded 

 on the surface of the inert substance, the surface tension of which it 

 alters in the same way as opsonin alters that of the bacteria. 



The degree of opsonization is determined to some extent by the 

 amount of salt present, and is found to be least (in the absence of 

 serum) in a i'2 per cent, solution ; hence this strength of salt is 

 used by some observers in opsonic determinations in order to 

 reduce the amount of spontaneous phagocytosis as low as possible. 

 Hamburger and Hekma have also shown that a minute trace of 

 calcium chloride has a great influence in increasing the opsonic 

 power of the serum (we have already seen that it aids the ag- 

 glutination of cholera vibrios), and that the activity of the serum 

 is increased by alkalis and diminished by acids. Chloride of 

 potassium, unlike chloride of sodium, has also an unfavourable 

 effect on the leucocytes. 



If we push our investigations a little farther, we may perhaps be 

 led to the belief that the amoeboid movements and protrusion of 

 pseudopodia which leucocytes display under suitable circumstances 

 may themselves be effects of surface tension rather than strictly 

 vital phenomena. Consider the case of the film of blood prepared 

 by Ponder's method, or by the use of a glass cell, as recommended 

 above. When this is incubated, large numbers of leucocytes 

 appear both on the lower and upper surfaces. Now in the latter 

 case the effect cannot be due to gravity, for the leucocytes are 

 heavier than the serum. It would be too great a strain on the 

 imagination to suppose the leucocytes capable of actual swimming 

 movements through the blood (and it may be remarked that many 



