148 Lectures on Bacteria. [§ xiii. 



are Cohn's and Billroth's works already mentioned (1, 6), and 

 those of von Recklinghausen and Klebs on the more specially 

 pathological side ; it is the merit of Klebs more particularly to 

 have clearly indicated not only the nature of the problem as 

 conceived by Henle, whom he expressly follows, but also the 

 details of the ways and methods to be adopted for its solution, 

 and to have pursued them himself, though sometimes perhaps 

 with more zeal than discretion. Pasteur and his school pursued 

 the same course independently. Thus questions and experi- 

 ments were framed and knowledge acquired with constantly 

 increasing precision and results. The latest advance to be 

 recorded begins with the participation of Robert Koch in the 

 work of research since 1876. He may claim to have gone 

 forward as a highly intelligent observer on the paths marked 

 out by his predecessors without precipitancy, and with careful 

 use of all improvements in morphological investigation and in 

 microscopical and experimental methods. Hence he was the 

 first to obtain clear results in cases which up to that time had 

 always been disputed, as is shown by our account in a former 

 lecture of the aetiology of anthrax, the final settlement of which 

 is due to his investigations ; he has also shown what must be 

 done to ensure progress in researches of this kind. 



The result of all these efibrts is the same as that which was 

 arrived at in plant-pathology thirty years before. Firstly, it is 

 certain that in a number of cases the contagium is a micro- 

 scopic parasite, and that certain diseases, the infectious nature 

 of which was formerly denied or was doubtful, are infectious 

 diseases of this kind. Secondly, the same conclusion is rendered 

 at least highly probable in other cases. Thirdly, there remains 

 a very considerable number of diseases in which the parasite 

 has been sought for, but has either not yet been found, or its 

 existence is doubtful. 



Further, it has been proved that, with some exceptions, 

 especially of skin-diseases and similar affections in which true 

 Fungi of a relatively large size are concerned, by far the most 



