552 Sir John Rose Bradford [May 30, 



of the last fifty years are the results of the discoveries of Pasteur in 

 this field. 



Reference was made to the important works of Leuwenhoek in 

 1683, Davaine in 1850, Koch in 1876, and Pfeiffer in 1892. 



In the last twenty years several diseases have been shown to be 

 due to quite large organisms only revealed by special methods of 

 staining or by special methods of microscopic technique. The 

 organism responsible for syphilis is a striking example of this, and 

 now with improved methods there is no insuperable difficulty in 

 demonstrating it when desired. Japanese observers have by some- 

 what similar methods succeeded in clearing up the causation of a 

 hitherto obscure form of febrile jaundice, and shown that it is due to 

 the presence of a spirochtete, an organism of very appreciable size, 

 and this Japanese work has been fully confirmed by other work 

 carried out on this disease amongst the troops in the B.E.F. 



There is, however, evidence available in support of the view 

 that some organisms are so extremely small as to be either 

 beyond the range of vision, or at any rate extremely minute, and 

 Pasteur himself suggested that future work might show that some 

 organisms were exceedingly small. This evidence is afforded by the 

 results of the use of filters in bacteriological work. Organisms 

 during their growth produce, like all living things, a number of 

 chemical products as a result of their vital activity. These substances 

 are often very violent poisons, and many of the symptoms of disease 

 are due to the direct action of these poisons on the tissues and organs 

 of the body. In order to study the processes of disease and of cure 

 it is essential to separate the organisms from their products and to 

 study separately the action of either the organisms, or of their 

 products on the experimental animal. Some of the most valuable 

 advances in modern medicine, and more especially in the treatment 

 of disease, have originated from discoveries made in this line of 

 work, and it will suffice to mention the treatment of diphtheria and 

 that of tetanus as illustrations. In both of these an essential factor 

 underlying the work was the separation of the poisons or toxins from 

 the organisms by the use of filters. Such filters must be of such a 

 nature that the pores of the filter are extremely small, as it is 

 essential for success that the organisms should not pass through. 

 Such filters are usually made either of siliceous earth or else of 

 unglazed porcelain, and many filters of different porosity, and usually 

 in the form of hollow candles, are on the market ; they differ greatly 

 in their efficiency and always require careful testing. It is usually 

 necessary to employ pressure in order to filter, and this may be 

 applied either as a positive pressure to the original fluid or preferably 

 by aspiration so as to suck the fluid through. The use of such filters 

 must be carefully controlled, and there are many sources of error and 

 possible fallacies, such as imperfections in the filter, the employment 

 of excessive differences of pressure, or too long a time being spent in 



