306 BACTERIA IN CROUPOUS PNEUMONIA. 



through many successive generations. As a rule, the different varieties, 

 which at first were seen to have the form of diplococci, when cultivated for 

 a length of time in artificial media presented the form of streptococci ; and 

 the elements which at first were lancet-shaped showed a tendency to become 

 spherical. 



The more virulent varieties usually presented the form of diplococci 

 with lancet-shaped elements, or of short chains. A variety which formed 

 long chains could be pronounced, in advance of the experiments on animals, 

 to possess comparatively little virulence. When by inoculations in animals 

 the virulence of such a variety was restored, the tendency to form chains 

 was less pronounced. 



Although, as a rule, no development occurs at 20 C. , certain varieties 

 were obtained which, after long cultivation in artificial media, showed a de- 

 cided growth at 18 C. 



Decided differences were shown by the cultures from various sources as 

 regards their growth in milk. Out of eighty-four cultures from various 

 sources eleven did not produce coagulation. ^ As a rule, cultures which caused 

 coagulation of milk were virulent for rabbits, and when such cultures lost 

 their virulence they usually lost at the same time the power of coagulating 

 milk. Virulent cultures die out sooner than those which have become at- 

 tenuated by continuous cultivation in artificial media; the first, on the sur- 

 face of agar, usually fail to grow at the end of a week, while the attenuated 

 cultures may survive for three weeks or more. 



Pathogenesis. This micrococcus is very pathogenic for mice and 

 for rabbits, less so for guinea-pigs. The injection of a minute quan- 

 tity 0.2 cubic centimetre or less of a virulent culture beneath the 

 skin of a rabbit or a mouse usually results in the death of the animal 

 in from twenty-four to forty-eight hours. The following is from the 

 writer's first published paper (1881), and refers to the pathological 

 appearances in rabbits : 



" The course of the disease and the post-mortem appearances indicate that 

 it is a form of septicaemia. Immediately after the injection there is a rise of 

 temperature, which in a few hours may reach 2 to 3 C. (3.6 to 5.4 F.); 

 the temperature subsequently falls, and shortly before death is often several 

 degrees below the normal. There is loss of appetite and marked debility 

 after twenty-four hours, and the animal commonly dies during the second 

 night or early in the morning of the second day after the injection. Death 

 occurs still more quickly when the blood from a rabbit recently dead is in- 

 jected. Not infrequently convulsions immediately precede death. 



"The most marked pathological appearance is a diffuse inflammatory 

 oadema or cellulitis, extending in all directions from the point of injection, 

 but especially to the dependent portions of the body. Occasionally there is 

 a little pus near the puncture, but usually death occurs before the cellulitis 

 reaches the point of producing pus. The subcutaneous connective tissue 

 contains a quantity of bloody serum, which possesses virulent properties and 

 which contains a multitude of micrococci. There is usutlly more or less in- 

 flammatory adhesion of the integument to the subjacent tissues. The liver 

 is sometimes dark-colored and gorged with blood, but more frequently it is 

 of a lighter color than normal and contains much fat. The spleen is either 

 normal in appearance or enlarged and dark-colored. Changes in this organ 

 are more marked in those cases which are of the longest duration. 



' ' The blood commonly contain s an immense number of micrococci, usual! y 

 joined in pairs and having a diameter of about 0. 5 /*. These are found in 

 blood drawn from superficial veins, from arteries, and from the cavities of 

 the heart immediately after death, and in a few cases their presence has been 



