1905.] On Spontaneous and other Phagocytosis. 221 



(a) If the so-called thermostable opsonins are in reality'thermostable, it will 



make no difference to the result whether the serum is heated in a 

 diluted or in an undiluted condition. If on the other hand the 

 thermostable opsonins represent nothing other than a residuum of 

 thermolabile opsonins which has escaped destruction by heat, it may 

 quite well happen that the serum will be completely inactivated if, 

 before the heat is applied, the serum is adequately diluted. 



(b) Again, if the serum as derived from an immunised organism contains in 



its native condition a mixture of opsonins, which are respectively 

 thermolabile and thermostable, we may, in conformity with the 

 all-round greater chemical stability of thermostable substances, expect 

 that the thermolabile opsonins will be destroyed when exposed to 

 sunlight, and that the thermostable opsonins will remain unaffected. 



(c) Lastly, if the reputedly thermostable opsonins constitute an altogether 



new and distinct category of opsonins produced in the course of 

 immunisation, we may expect, at any rate in cases where the immuni- 

 sation has been carried very far, to find the thermostable opsonins 

 greatly in excess of the thermolabile opsonins. In such a case it 

 would be reasonable to expect the heated serum to bear almost as 

 much dilution as the unheated serum before the point is in each case 

 reached where the opsonic power is lost. On the contrary, if the 

 so-called thermostable opsonins represent only an undestroyed 

 residuum of the ordinary thermolabile opsonins, we may expect the 

 heated serum to forfeit its opsonic power by dilution sooner than 

 the unheated serum. 



The graphic curves which are subjoined will serve to bring before the eye 

 the results of, in each case, a typical experiment instituted with a view to 

 the resolution of the questions suggested above. 



Curve 5 furnishes an answer to the questions suggested in (a) and (c); 

 Curve 6 an answer to the question suggested in (b). 



Explanation of Curve 5. — The experiment, whose results are here graphically 

 set forth, had a double object in view. Its first object was to determine 

 whether the tuberculo-opsonic power of the serum derived from an inoculated 

 patient would be only partially abolished in the case where heat is applied lo 

 the undiluted serum, and would be completely abolished when heat is 

 applied to the diluted serum. Its secondary object was to determine how far 

 one and the same serum could be diluted before and after heating before its 

 tuberculo-opsonic power was extinguished. 



The serum which was employed for the purposes of this experiment was 

 obtained from a patient whose opsonic index had been raised from - 17 to 



