IMMUNITY IN PNEUMOCOCCAL INFECTIONS 31 



In none of the rabbits immunised by pneumococcus did I obtain 

 an agglutinating serum. The serum of several cases of pneumonia 

 examined agglutinated the pneumococcus markedly, but in none were 

 such high dilutions as i in 40, i in 50, etc., obtained. In many cases the 

 addition of equal parts of a fine pneumococcal emulsion to serum, and 

 incubation for J-2 hours at 37° C, succeeded in demonstrating that 

 agglutination had taken place. On examining this microscopically, the 

 individual cocci seem to become swollen and run together into masses, 

 thus verifying the truth of Gruber's assumption of the swelling and 

 cohesion of the outer bacterial coats. The dilutions are best performed 

 by Wright's sedimentation pipettes, in which they can be quickly and 

 accurately performed and incubated at body-temperature. 



If an agglutinating serum be diluted i to 4, the agglutination 

 is not so marked as in the undiluted serum, and microscopically 

 also the appearance differs ; the deposit is not so granular. The 

 cocci do not appear so much swollen, and are joined together into 

 coiling chains — " the Fadenreaction." As shown by Neufeld, the 

 agglutinin is thermostable, but is destroyed by 100° C. It can withstand 

 60° C. for more than one hour. On healing the agglutinated cocci (in 

 the undiluted experiments) at 60° C. for an hour, the clumping and 

 swelling of the bacteria disappeared. 



As regards agglutination, in the Gruber-Widal sense of the term, the 

 cases examined lead to the conclusions : — 



1. That it is not present in every case of acute croupous pneumonia : 



it is very frequently absent altogether in cases which " crisis " 

 before the fifth day, and the longer the time till the crisis 

 occurs, the better is it marked. 



2. That the serum is very insusceptible of dilution, i 14 being 



considered as a high dilution. 



3. That it is essentially a critical phenomenon, appearing at, and 



disappearing soon after, the crisis. 

 The most recent addition to our knowledge of immunity has its origin 

 from the workers in the German University of Prague. Bail P) has 

 observed the great sensibility of tubercular guinea-pigs to fresh injections 

 of living tubercle bacilli. On intraperitoneal injection, the animals die 

 within a few hours, with an exudate in the pleural cavity, the cells 



(395) 



