lb 



that the immune serum had no measurable influence on the rate 

 of growth. 



Cocci from the peritoneal cavity of mice, which had been 

 immunised with 0*2 c.c. of serum one hour before the injection 

 of culture, grew in hanging drops at the normal rate. 



And in the peritoneal cavity of the immunised mouse the rate 

 of growth appeared to be normal. A mouse was given 0'2 c.c. 

 of serum and was inoculated with -culture 1-i hours afterwards. 

 The culture had been slowly centrifugalised for 5 minutes and 

 only the upper part (free from chains) was used. The rate of 

 growth was calculated by counting the number of pairs of cocci 

 per chain after 2, 60, 90 and 120 minutes. Apparently growth 

 continued until the chains or groups were overtaken by phago- 

 cytosis, and " the growth of some portion, at least, of the cells 

 " continues at a geometric rate." He observed that " capsule 

 " formation was marked in the peritoneal cavity of the immunised 

 " mouse, but in Type I pneumococcus infection this apparently 

 " interfered little with phagocytosis." 



Barber considered that the mechanism of passive immunity 

 was obscure. He did not think that agglutination was "of 

 " paramount significance " and he considered that " the exact 

 " importance of the property of facilitating phagocytosis has also 

 " not been thoroughly determined." 



He also made observations on the blood in acquired and in 

 natural immunity. The whole blood (diluted 1:11) and the 

 serum (diluted 1 : 5) of an immunised horse were tested in hanging 

 drops and in test-tubes. There was no difference in the rate 

 of growth between the immune blood and serum tests and the 

 controls. Similar results were obtained with whole, undiluted, 

 citrated blood. Hence he found no evidence that " inhibition of 

 " growth of pneumococci by serum or body fluids plays any part 

 " in acquired immunity." He compared, by the hanging drop 

 method, fresh, citrated, undiluted pigeon blood (1), with rabbit 

 blood (2). The growth in (1) was about one generation behind 

 (2); chains -were formed in (1) and discrete elements in (2). As 

 the result of further experiments, he found that " growth occurred 

 " about as often in the pigeon as in the rabbit blood, and the rate 

 " of groAvth in both was practically the same." 



In the preceding paragraphs I have confined myself to a statement of 

 American evidence for and against the application of an " antiblastic " 

 theory to pneumococcal immunity. An account of Ascoli's work and a 

 discussion of its significance are contemplated as part of the subject of a 

 subsequent report from me. 



Interrelationship of Types. 

 From what has been said in the preceding pages, it will be 

 noted that slight evidence of interrelationship may sometimes 

 be obtained by agglutination or precipitation tests or by immuni- 

 sation experiments on monkeys. The facts, however, which 

 stand out much more prominently, as the combined results of 

 experiments in vitro and in vivo, are (1) the sharp differences 



