296 TEMPERATURE AND OPSONIZATION 



slowly at 1 8 C. and rapidly at 37 C. Provided the bacteria 

 were sensitized at the latter, it mattered little or nothing whether 

 the mixture were incubated at either temperature, and a very 

 considerable amount of phagocytosis took place as low as 10 C. 

 Now at this point no movements of any sort occur, and it is quite 

 easy to satisfy oneself by actual observation under the microscope 

 that bacteria opsonized at 37 C. may be taken up at a low 

 temperature by bacteria which remain absolutely motionless 

 during the process. This is even more easily observed by using 

 a modification of a method recently introduced by Ponder, and 

 of very great value in the direct observation of phagocytic and 

 other phenomena. If a drop of blood be placed in a glass cell 

 about 0*2 millimetre deep (such as is used in mounting diatoms, 

 etc., in fluid), covered with a cover-glass, and incubated for fifteen 

 minutes or so, both slide and cover-glass will be found to be 

 dotted about with leucocytes which adhere so firmly that all the 

 red corpuscles can be washed off with warm normal saline solu- 

 tions, leaving the leucocytes adherent to the glass. If now the 

 cell be filled with serum mixed with bacteria, and incubated at 

 37 C., or with bacteria thus opsonized and thoroughly washed, 

 the process of phagocytosis can be readily watched, and is seen 

 to take place at 18 C. or lower. Under these circumstances, no 

 active movement or protrusion of pseudopodia takes place at all, 

 and it is easy to watch a sensitized coccus being gradually 

 attracted to and absorbed into the body of the leucocytes. The 

 process strongly recalls the agglutination of bacteria. A coccus 

 lying within a certain distance of the cell is seen, like the others, 

 to be in active Brownian movement, and the appearances would 

 suggest that it is slightly more easy for it to move towards the 

 cell than away from it. It oscillates in all directions, but 

 gradually approaches nearer and nearer the leucocyte, and is 

 finally taken in. Similar phenomena can be seen (using a hot 

 stage) when sensitized bacteria in an emulsion in normal saline 

 solution are added to leucocyte films at 37 C. ; and here also 

 no movement, or but little, takes place. If, however, serum be 

 added, there is usually some movement of the pseudopodia, but 

 little or no locomotion from place to place. 



It is not easy to determine whether phagocytosis may take 

 place in dead leucocytes. I have not been able to detect it in 

 leucocytes killed either by heat or cold, but Rosenau states that 

 when leucocytes killed in the former way are mixed with opsonized 



