108 Chapter V 



solidify when it is cooled. The ferment of the serum that produces 

 this effect resembles the precipitins in that it withstands the action of 

 a temperature of 56 C. and is only destroyed beyond 60 C. Like the 

 trypsins it acts in a weakly alkaline, neutral, or weakly acid medium ; 

 but digestion takes place best in a slightly alkaline medium. 



The question of especial interest to us is that of the origin of this 

 ferment which digests gelatine. If several c.c. of a 10 % solution of 

 this substance be injected into the peritoneal cavity of a laboratory 

 animal, there is provoked with certainty, within a few hours, a marked 

 leucocytosis of the peritoneal fluid. A considerable afflux of leuco- 

 cytes, amongst which the microphages are even more numerous than 

 the macrophages, takes place. When to a hanging drop of such an 

 exudation a trace of Ehrlich's neutral red solution is added, there 

 appears almost at once an intense coloration of the numerous droplets 

 inside the two kinds of leucocytes. It is, therefore, manifest that the 

 gelatine excites a powerful positive chemiotaxis of the mobile phago- 

 cytes and that it is absorbed by these cells. This experiment demon- 

 strates that the phagocytes can not only ingest solid bodies, such as 

 the various formed elements, coloured granules, etc., but that they are 

 also capable of absorbing fluid substances introduced into the tissues 

 or cavities of the organism. 



The data brought forward by Delezenne demonstrate very clearly 

 the part played by the mobile phagocytes in the digestion of gelatine. 

 He obtained his best results in the dog. We know that it is easy in 

 this animal to provoke an aseptic exudation, very rich in leucocytes. 

 This exudation when deprived of its serum and washed with physio- 

 logical salt solution gives a solution which exerts a feeble digestive 

 action on gelatine. If the exudation be produced in a dog that has 

 previously received several injections of this substance, we obtain 

 leucocytes whose extract, obtained by the same method, will digest 

 gelatine much more actively. The digestive power of the leucocytes 

 of the treated dog is sometimes five times greater than that of the 

 leucocytes of the normal dog. Here, then, we undoubtedly have an 

 acquired digestive power which reveals a great reinforcement of the 

 phagocytic activity. 



[116] In the prepared dogs the leucocytes have a much greater digestive 

 action on gelatine than has the blood serum of the same animals, a 

 fact which indicates that the source of the soluble ferment must be 

 sought for in the phagocytes themselves. The results of these 

 researches are of great service to us in the study of immunity 

 properly so called. 



