140 Transactions of the Society. 



getting far in the matter to roughly apply a bulb holding radium 

 salt to this or that tissue of plant or animal. More delicate 

 methods of experiment must be devised, and the simplest micro- 

 scopic organisms will probably be found to lend themselves to 

 the inquiry. 



Let me now pass to another question concerning bacteria, one 

 which we as naturalists and biologists might pursue on lines 

 somewhat distinct from those necessarily used by the medical man. 



The part played by bacteria in the alimentary canal of man 

 has become a very important matter of investigation. It is now- 

 attempted to check the activity of putrefactive bacteria which 

 require alkaline conditions for their activity, by introducing with 

 the food (as suggested by Metchnikoff) acid-producing bacteria, 

 those which produce lactic acid. Such lactic-acid-producing bac- 

 teria are taken in sour milk, and it has been certainly ascertained 

 that they do for a time establish themselves in the large intestine 

 and produce there an acid environment, which checks the growth 

 of certain putrefactive micro-organisms. The whole subject of the 

 microbian flora of the alimentary canal is under investigation and 

 demands an immense amount of further observation and experi- 

 ment. The condition of the alimentary canal of lower animals in 

 regard to bacterial activity is of great interest. It has been held 

 by some writers that the activity of bacteria is absolutely necessary 

 for the proper accomplishment of the digestive process in animals. 

 Metchnikoff has, however, shown that the large fruit bats (Ptero- 

 pus) of the East Indies have the digestive tract practically free 

 from bacteria, and that certainly bacteria do not take part in the 

 breaking up of food in that creature's intestine. The same fact 

 has been shown in regard to the digestion of some insects — experi- 

 ments having been made in which newly hatched larvse were fed 

 upon food devoid of bacterial germs. The subject, in so far as it is 

 one which is elucidated by the study of the smaller forms of animal 

 life, is one which is admirably suited to the efforts of the micros- 

 copist who works in his own study with simple apparatus. A 

 complete study of the bacteria to be found in the alimentary tract 

 of all animals, with a demonstration of the history and source and 

 activity of such bacteria as are found, is required. Even amongst 

 the Protozoa we find intrusive "bacteria" taking part in the life- 

 processes of their hosts as a normal thing. The " rodlets " described 

 by Greef in his original account of the amoeboid Pelomyxa — as a 

 constituent part of the organism — are very abundant and were 

 regarded as crystalline needles. They were, however, not present 

 in a new species of Pelomyxa discovered by Professor Bourne in 

 Madras, although invariably found in the European Pelomyxa palus- 

 tris. Fourteen years ago these rodlets were shown in my laboratory 

 at Oxford to be bacteria, and were cultivated by Mr. Hill, now of 

 Eton College. Among the Ciliata, bacteria occur in a more excep- 



