13 



and vaccine vesicles. It was obvious that the contagium 

 existed in the liquid, but what was its nature ? By a careful 

 series of experiments he was able to filter out solid granular 

 matter from the liquid portion, and to ascertain that this 

 granular matter alone contained the poison. These granules, 

 according to Sanderson, consist of transparent particles from 

 the 50,000th to 20,oooth of an inch in diameter. 



Little further advance was made until 1S65, during 

 the inquiries of the Cattle Plague Commission. Ur. Lionel 

 Beale then stated that swarms of extremely minute particles 

 were found present in the textures and juices of the infected 

 animals, and these he believed to be the contagiuui of the 

 disease. 



In the following year Rindfleisch showed that the 

 minute metastatic deposits sometimes seen in the heart in 

 cases of pyaemia and other infective diseases were not really 

 abscesses as they had hitherto been considered, but were 

 really aggregations of vibrioncs. Not to weary you with too 

 much detail, I may say at once that since that time minute 

 organisms have been found to be associated with a consider- 

 able number of diseases such as Diphtheria, P3Demia, 

 Puerperal Fever, Typhus, &c. 



You will say, no doubt, that the mere presence of 

 organisms in these cases, does not prove that they acted as 

 causes. Their existence may have been altogether acci- 

 dental, or they may have appeared late on the scenes merely 

 as parasites, in a material undergoing, or ready to undergo, a 

 sort of decomposition. The truth can only be discovered by 

 observation and research. Now obviously the necessary 

 experiments can only be conducted on the lower animals, and 

 so many diseases must be left untouched, but if the truth of 

 the proposition can be established in one or more cases, it 

 becomes more and more probable for the rest. Let us now 

 examine the evidence. 



As I said before, the investigation of this question is 

 attended with the greatest difficulty ; not only must the 

 highest powers of the microscope be employed, but special 



