206 MICROBES AND TOXINS 



abnormal and yet one knows that it is only in abnormal conditions 

 that the leucocytes discharge complement. " The least change 

 in the salt content of the surrounding fluid is sufficient to 

 modify notably the phagocytosis. The leucocytes, of patients 

 suffering from various diseases present a marked, diminution 

 in their vital activities. The destruction of bacteria is 

 the work of phagocytes which are living and vigorous" 

 (Metchnikoff, Nobel Lecture). Washing, chilling, maceration 

 are quite sufficient to destroy the complement of the leucocytes ; 

 how is it possible to conclude after such procedures that the 

 leucocytes do not contain the complement ? 



The opponents of phagocytosis declare that it is the humoral 

 properties which undergo the most marked increase during 

 immunization. There is no doubt of such a development of 

 bacteriotropins, opsonins and immune-bodies — ^which in any 

 case are phagocytic products. But it can be shown experi- 

 mentally that the phagocytes are modified in immunity and 

 modified sooner than the body-fluids. Leucocytes taken from 

 an animal vaccinated against some microbe and injected into 

 a fresh animal protect the latter from several lethal doses 

 of the microbe, whereas the leucocytes of a normal animal fail. 

 (Pettersson's experiment). The white corpuscles of the 

 immunized animal supply protective substances at a time when 

 the blood-fluids are not yet affected : and it is owing to the 

 leucocytes that the body remains refractory after the body 

 fluids have already lost their protective properties (Salimbeni). 



Serum is a fluid into which have been poured the ferments 

 of the lencocytes, the fibrin-ferment and the complement. 

 Injury to the leucocytes is necessary before blood will coagulate. 

 By very delicate operations and with great trouble it has been 

 possible to separate the blood corpuscles and obtain a 

 plasma which remains — for a certain time — incoagulable. 

 Now the properties of such plasma are very different from 

 those of serum : the leucocytic excretions are absent. It is, how- 

 ever, so difficult to obtain a true plasma identical with that of 

 the circulating blood that such experiments have to be very 

 carefully analysed. When quickly prepared immediately after 



