president's address. 5 



already formed in the body -fluids to a certain extent, and assist 

 in the maintenance of health. An increased quantity of opsonin 

 in the body may be produced hy the injection of dead bacteria 

 or by the consumption of yeast. 



Since dead bacteria and yeast can increase the opsonic content 

 of the bluod, the question arises, are the opsonins produced 

 ■directly from the bodies of these micro-organisms, or are they 

 formed indirectly in response to a stimulus given by their pro- 

 ducts of digestion 1 Experiment showed that they are not 

 formed directly, from which it follows that their products of 

 digestion stimulate the activity of some opsonin-producing organ. 



It is a curious fact about the action of opsonins that by 

 diluting fresh blood serum we obtain an increase in its opsonic 

 activity. The reason was not known until investigations were 

 undertaken in the Society's laboratory. As a result of much 

 experimentation, it appears that the cause of the phenomenon 

 lies in the activity of the phagocytes. The salinity of normal 

 blood serum is too high for a maximum phagocytosis, and there- 

 fore by weakening the percentage of salt, the gradual dilution 

 brings the serum to a point at which the phagocytes can work 

 best. From this point a further dilution lessens both opsonic 

 content and phagocytic activity. Less important factors in con- 

 trolling the phenomena are the relative abundance of bacteria to 

 be ingested, the nature of the phagocytes, and the duration of 

 the period of contact between opsonised bacteria and phagocytes. 



In the domain of economic bacteriology. Dr. Greiir-Smith 

 investigated the cause of the thickening of condensed milk. In 

 our climate it is not unusual to find that a thickening has taken 

 place during storage. When the tins are opened by the public, 

 the milk may be thick, lumpy, or like a stiff jelly. The cause of 

 this condition was traced to a micrococcus which apparently 

 •obtains access to the milk either during cooling or canning, and 

 slowly coiigulates the casein by secreting a rennet-like ferment. 

 The small quantity of air remaining in the tin probably assists 

 the growth of the bacterium. The microbe is easily killed, and 

 there appears to be no reason why greater care in the later stages 



