268 MEDICAL BACTERIOLOGY 



antitoxin received from the mother before birth and lost during the first 3 

 months of life but gradually replaced by the possessor's own cells and apparently 

 without the stimulus of infection. 



Rabbits normally possess agglutinins for pneumococci but after inoculation 

 with sublethal doses of pneumococci they develop more abundant, and, there- 

 fore, more effective pneumococcus agglutinin. Bull has found that pneumo- 

 cocci injected intravenously soon disappear from the circulation as a result of 

 agglutination. If sufficient numbers are injected the natural agglutinin is 

 exhausted and cocci escaping destruction lodge in tissue and multiply. After a 

 time, stimulated by the infection, more agglutinin is produced and coincident 

 with the appearance of acquired agglutinin recession of the disease begins. 



In addition to the antibodies that have been demonstrated and described, 

 there are others, possibly of equal importance in the establishment of immunity, 

 that are still obscure. Sclavo's serum which unquestionably possesses immuniz- 

 ing power contains little or no opsonin, complement, lysin, agglutinin, antitoxin, 

 precipitin or cytase. It is observed at times that serum containing no demon- 

 strable antibodies from an immune animal will prevent the multiplication of 

 bacteria without otherwise affecting them. 



THEORIES OF IMMUNITY 



After more than a quarter of a century of research and observation of the 

 phenomena accompanying infection and immunity in various animals from the 

 simple unicellular forms up to and including man, Metchnikoff concluded that 

 invading organisms exert varying degrees of chemiotaxis; some a negative 

 chemiotaxis, others a slight positive and some a strong positive chemiotaxis on 

 the phagocytic cells of the host. In the mammals this action is exerted on 

 certain body cells and is most strikingly exemplified by the chemiotaxis of 

 some bacteria for leucocytes. 



He believed the production of cytase and other antibodies, above and in 

 addition to what normally exists, depends upon two factors: stimulation of the 

 cells of the host by the invading organism; and an increased production of 

 cytase, agglutinin, lysin, etc., by the cells stimulated, the increase being in 

 quantity or quality or both. 



Metchnikoff considered digestion of bacteria within the phagocytic cells of 

 the body the ultimate and also the essential process in ridding the body of 

 bacteria. He believed excretory organs in a normal condition never excrete 

 bacteria. He assumed that the action of antibodies in the blood serum on 

 bacteria facilitates their ingestion and digestion by phagocytic cells but con- 

 sidered bacteriolysis an exclusively intracellular phenomenon. 



The observations of some of his contemporaries and followers have amply 

 confirmed some of Metchnikoff 's views and discredited others. It is now recog- 

 nized that the establishment and maintenance of active immunity and the con- 

 quest of infection is a matter of cellular activity; in some cases the activity of 

 phagocytic cells and in other cases the activity of cells, (not phagocytes) that 

 emanate antibodies which flow in the blood serum and attack, arrest or destroy 

 bacteria or neutralize their toxins. 



