DIPLOCOCCUS PNEUMONIA 367 



No headway has been made up to the present time with similar 

 treatment against Types III and IV. 



Occasional favorable results have been obtained by Hiss in the treat- 

 ment of pneumococcus infection in animals, and by Hiss and Zinsser 1 

 in the treatment of pneumonia in man with aqueous leucocyte extracts. 

 Although this work has not been extensively followed and has been dis- 

 appointing in late years, there is no doubt in the mind of the writer 

 that individual cases have been favorably influenced. The writer be- 

 lieves (differing from an opinion expressed in earlier papers) that the 

 influence of such leucocyte extracts (as, it might be incidentally stated, 

 he believes the influence of intravenous injections of bacteria in typhoid 

 and other conditions) consists in its chemotactic influence, i.e., its ten- 

 dency to increase circulating leucocytes. The contrast between the good 

 results in rabbits and the less striking results in man may easily be due 

 to the fact that in rabbits intravenous injections were practiced. 



Differentiation of Pneumococcus from Streptococcus. Pneumococci 

 and streptococci which do not differ in morphology from their classic 

 types can usually be differentiated from each other and identified by 

 their morphological characters without difficulty; but* it is equally true 

 that certain cultures of these organisms, either at the time of their 

 isolation or after cultivation on artificial media, approach the type of the 

 other so closely that it may be impossible to identify them by their mor- 

 phology alone. When such morphological variations occur there are no 

 constant cultural or pathogenic characters as yet demonstrated which 

 distinguish between these organisms. 



This lack of distinct cultural differences between pneumococci and 

 streptococci has not infrequently led to confusion, and that uncertainty 

 should exist and mistakes be made in identification is not surprising 

 when one considers the characters usually depended upon to distinguish 

 pneumococci from streptococci. Chief among these, as has just been 

 implied, are the morphological features which are, in the case of pneu- 

 mococci, a slightly lancet or elongated form rather than the more typical 

 coccus form characteristic of the streptococci, and an arrangement of 

 such cocci in pairs rather than in chains; added to these features is the 

 possession of a more or less well-defined capsule. All of these char- 

 acters are subject to variation or may be absent. Compared with the 

 morphological, the cultural characters are variable and of minor im- 

 portance. The pneumococcus colonies on coagulated blood serum and 



1 Hiss and Zinsser, Jour. Med. Res., xix, 1908. 



