440 LIFE : OUTLINES OF GENERAL BIOLOGY 



chemical entities, for they may be properties of the colloidal equi- 

 librium of the blood and its cells. Their effect may be physico- 

 chemical rather than chemical. But no one doubts their reality. 



THE BACTERIOPHAGES- This unfamiliar word refers to an 

 interesting discovery made by Dr. D'Herelle, of the Pasteur Insti- 

 tute, — a discovery (1918) which stands for something new, even if 

 it does not turn out as the investigator expected. Bacteriophage 

 means bacterium-devourer, and D'Herelle's theory is that we have 

 normal partners which destroy some of the bacteria that invade our 

 l)odies. A bacteriophage is a living organism of extreme minuteness, 

 far smaller than an average bacterium—a Hfe-size diagram of which 

 may be seen with a good lens inside the second "o" of the word 

 good. The particular species which D'Herelle discovered in 1918 is 

 called Bacterium intestinale, and this tells us where it lives. Some 

 fierce critics say that its name should be "mare's-nest", but that is 

 not fair to D'Herelle, who has certainly discovered a phenomenon, 

 whether his interpretation be right or wrong. 



What is D'Herelle's phenomenon? If a few bacteria of the pyo- 

 cyanic species be added to a culture of dysentery bacteria they 

 multiply and produce ferment-like secretions dissolving the wulent 

 bacteria amongst which they have been introduced. But D'Herelle 

 found that when a clear filtrate is made of some of the debris from 

 the food-canal of a convalescent dysenteric patient (a filtrate that 

 is quite limpid and passes through a porcelain filter), it has a rapid 

 solvent effect when introduced among the dysenterj' microbes. It 

 can be multiplied indefinitely; its ]X)wer is not lessened by dilution; 

 it behaves as if it contained microbes. In carefully controlled condi- 

 tions it will form spots on a gelatine plate, and if a jilatinum thread 

 be drawn through one of these spots and then placed in a culture 

 of dysenteric bacteria the result is a rapid solution of the latter. 

 In indirect ways it has been found possible to estimate the size of 

 the invisible corpuscles that D'Herelle regards as Bacteriophages. 

 They are ten times smaller than the smallest bacterium visible 

 under the microscope; but they are several times larger than the 

 invisible germs of the ultra-virus disea.ses. such as foot-and-mooth 

 dis<\ise. 



Perhaps D'Herelle's phenomenon is due to something like an 

 anti-toxin, which is almost like an "x". But it seems impossible at 

 present to prove that he is wrong in ascribing it to the agency of 

 a living organism (his Bacteria phaf^um intestinale) which is part of 

 man's normal Iwdyguard. His picture is an interpretation of facts. 

 It leads us to think of extremely minute and very useful symbions, 

 living in our food-canal, producing a secretion of high opsonic 

 potency, which educates the phagocytes and prepares injurious 

 bacteria for death. Organisata non sunt multiplicanda pr.Tter 



