40 ' 



These experiments show that the washed cocci and the 

 clear peritoneal washings each precipitate the protective sub- 

 stances from immune serum but without destroying their pro- 

 tective properties. Is this evidence that the substances are 

 bacteriotropic in nature and form a loose combination with the 

 absorbing cocci ? 



The following experiment appears to indicate that, if any 

 combination occurs, it must be a very loose one. 



A mixture was made of 1 c.c. of Type I serum and 0*01 c.c. of living 

 Type I broth culture, and was allowed to stand in the ice chest overnight. 

 The next day, the mixture was well shaken, and small amounts, repre- 

 sent ina a mixture of 0*01 c.c. of serum and 0*000 1 c.c. of culture down 

 to 0*000 001 c.c. of serum, and - 000 000 01 c.c. of culture, were inocu- 

 lated into mice. All the mice survived. The remainder of the mixture 

 was centrifuged, and the serum was poured off. Fresh serum was added 

 to the deposit : after a few hours this was poured off, and the deposit 

 was washed. The deposited cocci, which were now presumably sensitised, 

 were resuspended in broth, and were inoculated into mice in doses estimated 

 to contain from 0*000 001 c.c. to 0*000 1 c.c. of broth culture. One of 

 three mice died of pneumococcal septicaemia, two survived. 



The first part of the above experiment was repeated with the same 

 amount of serum but ten times the amount of culture, i.e., 1 c.c. serum to 



* 1 c.c. culture. The mixture of serum and culture was inoculated into 

 mice as before, and all the mice survived excepting the one which received 

 the smallest amount of culture and of course the smallest amount of serum. 



The above results would seem to indicate that the cocci 

 were not sensitised, but that the mice which survived owed 

 their protection to the serum inoculated along with the culture ; 

 in the case of the highest dilution of the mixture the amount 

 of serum was inadequate to give any protection, even against 

 the minute dose of culture. 



The following experiment supports this view. The centrifuged deposit 

 from the above mixture was washed with broth and was resuspended. All 

 the mice died after inoculation with amounts estimated to contain from 

 0*01 c.c. to 0*000 001 c.c. of broth culture. 



The action of culture on an immune serum in the animal 

 body is apparently different from its action in the test-tube. 

 It was found in the former that the effect of the intravenous 

 inoculation of culture into an immune animal was to abolish 

 temporarily the protective power of the serum. This circum- 

 stance may perhaps help to explain the occurrence of endocarditis, 

 following the inoculation of living culture, in rabbits which have 

 been highly immunised with killed culture. It has happened 

 frequently, see p. 22, and with every type of pneumococcus, 

 in spite of the fact that the serum of the rabbit was capable of 

 conferring protection on mice. One can imagine that the tem- 

 porary inhibition of protection, as a result of the inoculation, 

 enables the pneumococci to establish themselves on the avascular 

 cardiac valves. 



Absorption of Protective Substances. 

 Several absorption experiments have been done with Types 



1 and II sera, and it has been shown that, by treatment with the 



