318 INFECTION AND RESISTANCE 



Cowie and Chapin. 29 Dean 30 had previously shown that, although 

 heated immune serum was capable of exerting opsonic action by 

 itself, this action could nevertheless be enhanced by the addition of 

 a little diluted fresh normal serum. The particular significance of 

 Dean's work will be discussed later. Cowie and Chapin, however, 

 carried on similar experiments with normal serum in which they at- 

 tempted to reactivate heated normal serum by the addition of small 

 amounts of diluted fresh serum, by itself but slightly opsonic. One 

 of their experiments may serve to illustrate this point, as follows : 



Experiment 10. June 13, 1907 



Phagocytic 

 count 31 



1. Unheated serum 15 . 44 



2. Salt solution 0. 18 



3. Heated serum, 57 C 1 .08 



4. Diluted serum (1 :15) 1 .56 



5. Heated serum 57 C. + diluted serum (1 :15) 12 . 40 



6. Unheated serum + unheated serum 16 . 08 



This experiment and others like it seem to demonstrate clearly 

 that the opsonic action of normal serum, though dependent largely 

 upon alexin, is nevertheless also dependent upon a heat-stable body, 

 comparable to the sensitizer or amboceptor, in that it is reactivable to 

 almost the full power of the original condition (before heating) by 

 slight amounts of alexin in themselves almost inactive. 32 



These findings were later confirmed by Eggers, 34 and it is plain 

 from this work that the apparent opsonic inactivation of normal 

 serum by heat depends upon the destruction of the heat-sensitive 

 constituent only the heat-stable substance surely involved in the 

 process, remaining intact, and reactivable. 



Closely associated with this phase of the problem is that of the 

 specificity of the normal opsonins. For if, as at first supposed, the 

 normal opsonins are, like complement or alexin, non-specific, the 

 above amboceptor-complement structure of this mechanism would 

 be rendered unlikely. Earlier work upon this question was con- 

 tradictory. Bulloch and Western, 35 working with staphylococci and 



29 Cowie and Chapin. Jour. Med. Ees., Vol. 17, 1907, pp. 57, 95 and 

 213. 



30 Dean. Loc. cit. 



31 Phagocytic count = average number of bacteria in each leukocyte. 



32 In earlier experiments Hektoen and Ruediger 3S did not succeed in 

 reactivating heated sera and concluded that normal opsonins had the hypo- 

 thetical structure of toxins in that they possessed a haptophore and an 

 opsonophore group. From this point of view Hektoen has subsequently 

 receded largely because of work done under his own direction. 



33 Hektoen and Ruediger. Jour. Inf. Dis., 1905. 



34 Eggers. Jour, of Inf. Dis., Vol. 5, 1908. 



35 Bulloch and Western. Proc. Roy. Soc. B., 77, 1906. 



