BLOOD AND THE IDENTIFICATION OF 

 BACTERIAL SPECIES. 



THE identification of any particular bacillus may be 

 either a very easy or a very difficult matter. The 

 detection of tubercle bacilli in sputum can be pretty safely 

 entrusted to any conscientious medical student who has 

 done his course of practical pathology : the determination of 

 typhoid bacilli in the excreta of a patient may require all 

 the resources of an experienced bacteriologist. During 

 the last two years, however, the development and proper 

 understanding of previous isolated or misinterpreted obser- 

 vations has given us a new and generally trustworthy 

 method of recognising many species of micro-organisms. 

 And more than this, by a simple reversal of the procedure 

 it has been possible to supply a new means and aid to 

 clinical diagnosis — another addition to practical medicine 

 derived from experimental science. 



So for back as 1889 Charrin and Roger (3) demon- 

 strated that the growth of B. pyocyaneus (and of other 

 bateria) differed when made in the serum of animals im- 

 munised against B. pyocyaneus and when made in the 

 serum of normal animals. The differences consisted in (i.) 

 serum remaining more transparent, (ii.) formation of granu- 

 lar agglomerations and (iii.) microscopically, the formation of 

 chains of altered bacteria, in the former mode of cultiva- 

 tion. 



In 1 89 1, Metschnikoff, whilst investigating Vibrio 

 Metschnikovi, saw the same phenomena, and noted them 

 as facts requiring further investigation (10). But he made 

 no progress in this direction, being discouraged by failure 

 to obtain the reactions with the bacillus of hog cholera. 



In 1893 Issaeff made similar observations with Pneu- 

 mococci, and later in conjunction with Ivanoff, with 

 Vibrio Ivanovi. They attributed the effects obtained 

 to the bactericidal and growth-hindering substances in the 

 serum (8). 



