^ XII.] Anthrax. 135 



grounded objections to the praises bestowed on the school of 

 Pasteur. We cannot enter further in this place into these prac- 

 tical questions. The fact, however, of the frequent success of 

 protective inoculation is well established, and is abundantly con- 

 firmed even by those who are opposed to the exaggerated 

 estimate of its practical importance. We record it therefore as 

 a phenomenon of high scientific interest. 



Having now become acquainted with these phenomena relative 

 to Bacillus Anthracis and the disease which it produces, let us 

 enquire how the injurious effects of the virulent Bacillus are 

 brought about, and how the attenuation of the virulence and the 

 operation of protective inoculation just described are to be 

 explained. 



In the present state of our knowledge we shall succeed in 

 answering these questions best if we begin with the second. To 

 prevent misunderstanding I will say beforehand most distinctly, 

 that we can at present only make an attempt to answer these 

 and all other questions, and must wait for our answers to be 

 confirmed or amended by future investigation. 



We begin therefore with the question of the explanation of 

 protective inoculation, and we may formulate it a little differently 

 and extend it by asking how it is that an animal is or becomes 

 unsusceptible to, safe from the attacks of the injurious parasite. 

 Metschnikoflf has lately published some investigations which, if 

 confirmed, bring us a step nearer to the understanding of this 

 phenomenon. I report them because they seem to be trust- 

 worthy ; I have not been able to repeat them myself. 



We know that the blood of vertebrate animals contains red 

 blood-corpuscles suspended in the fluid blood-plasma, and be- 

 sides these colourless or white blood-corpuscles or blood-cells 

 in considerably smaller quantity. The lower animals have no 

 red blood-corpuscles, only the colourless blood-cells, which are 

 uncoloured nucleated protoplasmic bodies. They possess a 

 variety of remarkable qualities, but at present we are chiefly 

 concerned with the fact that, like many other protoplasmic 



