208 THE PRESENT EVOLUTION OF MAN — PHYSICAL 



duced. Here again tlicse special chemical products 

 could not be detected in the blood, and must have been 

 present in such infinitesimally small quantities, that it 

 is difficult to see how they could exert any very marked 

 influence on the activity of the bacteria ; whilst, as 

 Flugge points out, our knowledge of the actions of the 

 tissues on foreign bodies of various kinds would lead us 

 to the conclusion that any such material would be very 

 rapidly eliminated. Then Grawitz suggested that in 

 any battle between the cells and the bacilli that may 

 occur in the body during the course of a disease, if the 

 cells can but manage to obtain the upper hand and to 

 destroy the bacteria, they should become hardier, as it 

 were, through the training of the contest, tlieir vital 

 energy and assimilating j3ower should be increased, 

 and they should thus become able to deal in a more 

 summary manner with any organisms with which they 

 mioht afterwards be brought in contact. Then came 

 Buchner's theory of the inflammatory cause of immunity, 

 which offered another explanation. He argued that 

 bacteria made their way into the body at certain 

 special points, these points, seats of infection, differing 

 in different diseases, and that in consequence of the 

 development of the bacteria, there was a reactionary 

 alteration, inflammatory in its nature, in the tissues, 

 which fitted them for the future to resist the special 

 organism that had previously made the attack ; this 

 minute alteration in the function of the special cells at 

 the seat of the invasion enabling them to resist the 

 further action and invasion of the same organism even 

 at a considerably later period. Again, based on the 

 same principles as Grawitz's theory, came the now 

 celebrated Metschnikoff theory. Metschnikoft' holds 

 that the protection against the attacks of micro- 

 organisms on the body is entirely due to the action of 

 the amoeboid cells of the body ; that these cells are 

 living pieces of protoplasm ; that they are constantly 

 taking into their own substance all foreign particles 

 which find their way into the body ; that wherever there 

 is an extra demand on their energies, a large number 

 are attracted to the point at which the work is to be 



