32 STUDIES IN IMMUNITY. 



increase of the organisms. Preparations from these fluids are even 

 more striking than the plates; they show. a large number of or- 

 ganisms in the edema fluid, very few in serum "A," and still 

 fewer in serum "B." It is also to be noted that the colonies 

 grow more rapidly on the plates inoculated with edema fluid than 

 on the other plates. 



The increase in bactericidal property in the blood following the 

 injection of normal serum would appear to be due to a reaction on 

 the part of the leucocytes and not to an increase in the number of 

 cells in the blood, as it is not accompanied by a hyperleucocytosis; 

 on the contrary, the number of white corpuscles is found to be 

 slightly decreased. Another similar experiment was performed 

 with bouillon in place of normal serum. The same result was 

 obtained, and in the same way there was no increase in leucocytes 

 noted in the blood (8400 before the injection and 7400, 24 hours 

 after injection). 



There are certain undoubted conclusions that may be drawn 

 from these experiments. // the number of leucocytes in the blood is 

 diminished during life, the blood is found to be less bactericidal. The 

 blood plasma, more or less completely separated from the cellular 

 elements within the body, has less bactericidal property than the whole 

 blood. The separation of the fluid from the cellular part of the 

 blood outside the body by coagulation does not bring about the 

 same result. The serum of vaccinated animals although deprived 

 of cells is energetically bactericidal. We shall take occasion to 

 elaborate these results later. It seems reasonable to admit not 

 only that bactericidal substances are present in leucocytes, but that 

 when the blood has been removed from the body the white cor- 

 puscles soon discharge into the serum those bactericidal substances 

 which under normal conditions they retain within themselves. This 

 would explain why the bactericidal property of body fluids which 

 is so marked in vitro is much less evident during life. This latter 

 fact has been particularly well brought out by Metchnikoff, and 

 indeed it is notorious that results obtained in vitro do not always 

 exactly indicate what goes on within the animal body. Phagocytes 

 have an efficient and rapid means of destroying the bacteria they 

 have taken hold of. The evidence of the effect of phagocytic 

 secretions on many organisms, particularly on cholera vibrios, is 



