202 Cliapter VII 



which in several respects approximate to the trypsins, have this 

 further feature in common with them that they can act without the 

 help of any fixative ? It is known, as mentioned in Chapter III, that 

 trypsin can digest alone, or in collaboration with enterokynase, that 

 ferment of the intestinal juice which acts as such a powerful ad- 

 [2i3]juvant to the pancreatic ferments. Is this also the case with the 

 cytases ? The fact that when Proteus vulgaris is placed in contact 

 with normal unheated guinea-pig's serum, it is incapable of absorbing 

 cytases, although it is so readily digested by phagocytes, indicates 

 rather that, for the fixation of cytases, the help of the fixative is 

 indispensable. But, as this fixative is absent from the serum, and 

 since, nevertheless, it must exist for the needs of digestion, it must 

 clearly be concluded that it is found inside the phagocytes. Its 

 quantity is perhaps so small that when it has passed into the serum 

 its action is entirely lost or nearly so. Fresh researches are necessary 

 to elucidate this delicate point. 



But perhaps the phagocytes which, as we have just seen, can 

 engage in a struggle with and ingest the micro-organisms without the 

 latter being previously modified by the fixative, may be incapable 

 of fulfilling their functions without the help of some other substance 

 circulating in the blood plasma? Amongst these substances is one 

 which manifestly acts upon the micro-organisms by rendering them 

 motionless and agglomerating them into masses. This agglutinative 

 property is met with in the normal fluids of many species of 

 animals and is exercised upon many bacteria. It may be demon- 

 strated not only in the blood serum, but also in the fluids of 

 transudations and exudations and in certain secretions such as 

 milk, tears, and urine. Little is known as yet of the mechanism of 

 this agglutinative action, and we can the more readily refrain from 

 entering into details concerning it as it is of no great importance 

 from the point of view of natural immunity. 



In the preceding chapter we have already spoken of the ingestion 

 of cholera vibrios in the peritoneal cavity of guinea-pigs. In those 

 cases in which the animals exhibit an effective resistance, the 

 phagocytes devour the vibrios whilst they still exhibit very active 

 movements. Even when a large majority are already seized by the 

 leucocytes and only a few isolated free vibrios remain, these latter 

 still continue to exhibit normal movements. These facts, repeatedly 

 observed, clearly demonstrate that phagocytosis may take place 

 without any previous agglutinative action ; this does not, however, 



