282 ALTERNATIVE EXPLANATIONS 



products thereof, causes a sharp rise in temperature and an 

 inflammatory process around the tuberculous focus. If the dose 

 of tuberculin be greatly reduced the local reaction takes place, 

 but there is no rise of temperature. This is best seen when 

 small doses of TR are used in the treatment of tuberculous 

 iritis, in which the iris can often be seen to become injected after 

 each dose ; and I have observed the same reaction in a very 

 marked form after the use of diluted old tuberculin in von 

 Pirquet's reaction. In this case the dose absorbed must have 

 been infinitesimal, since the temperature did not show the slightest 

 sign of a rise. 



Other possibilities are that the vaccine may cause a general 

 tissue immunity, or that it may produce some degree of immunity 

 on the part of the leucocytes, or may at least alter them in some 

 way so that they are more able to perform their duties as phago- 

 cytes ; and, of course, other antibodies, such as antiendotoxins, 

 may be produced as a result of the injection, and of these the 

 opsonic index affords us no estimate. 



In reverting to the question of the nature and properties of the 

 opsomns, the question of their thermo-stability first claims our 

 attention. The results obtained by various observers are not 

 quite in accord, and indicate very clearly that more than one 

 substance may have the same action. The opsonin present in 

 normal serum is in a high degree thermolabile. It is destroyed 

 by heating to 55 C. for half to one hour ; at 60 C. most disappears 

 in five minutes, the rest more slowly, little being left in fifteen 

 minutes. Wright and Reid, however, found that in cases of 

 tuberculosis some of the opsonin is more thermostable, and 

 whereas in heating a normal control to 60 C. for ten minutes 

 reduces the opsonic index to almost nothing, the same proceeding 

 may only lower the index of a tuberculous serum to 0-4 or so, 

 though the indices of both samples were formerly the same. 

 They suggested this as a means for the diagnosis of tubercle. 

 Other observers have failed to corroborate their results, and they 

 are certainly not true of all cases. Dean showed that in certain 

 sera obtained by the high immunization of animals to certain 

 bacteria (staphylococci, dysentery, and typhoid bacilli) there are 

 substances which act as opsonins, and which are thermostable. 

 His results have been corroborated for pneumococcic serum by 

 Macdonald and Rosenau, by Muir and Martin, and many others. 

 It is evident, therefore, that there is more than one substance 



