IxXVi PROCEEDOGS OF THE GEOLOGICAL SOCIETY. [May I 899, 



or oxidized Loam, and sand, with a sufficient quantity of 



vegetable mould, are the best soils.' ^ 



As sand is also a water-bearing earth, it is clearly essential that 

 any burial-ground on it should be so placed that either the water 

 from the latter shall not flow toward any wells, or, if it does, that 

 there should be an ample amount of disinfecting earth between. 



Some bacteriological experiments made by Dr. Klein during last 

 summer are of much interest in showing the powerful filtering effect 

 possessed by fine compact sand. Through his kindness I am able 

 to give the results of these unpublished experiments, in a condensed 

 form. They were made on Thanet Sand from near Croydon, a sand 

 so firmly compacted that it stands with a practically vertical and 

 even face in section, and remains thus for a long time. 



The specimens were taken at a depth of about 6| feet, and were 

 found to be practically sterile, showing that the superincumbent 

 layers had acted as a good filter in keeping out the many microbes 

 present in the soil. 



Experiments on filtration made in the laboratory proved that even 

 under the most favourable conditions, such as do not occur in nature, 

 the passage of microbes through a thickness of 20 inches of the 

 sand is extremely slow. In these experiments, on four occasions, a 

 whole culture of special bacteria was poured on to the top of the filter. 

 Such a culture yielded an amount of bacterial matter that could 

 hardly be expressed by many millions of bacteria. Yet only after 

 30 days' continuous filtration did the first bacteria appear in small 

 numbers in the filtrate. 



Considering the amount of culture added on the top and the 

 slowness with which the first traces appeared in the filtrate, it is 

 justifiable to assume that we have not simply a passage or filtra- 

 tion, but an actual growing- through of the bacteria. This really 

 happens, under similar experimental conditions, both with the 

 Pasteur and with the Berkenfeld filters, which are the most perfect 

 of their kind ; and, moreover, it happens under less rigorous con- 

 tinued filtration than in the experiments with the sand. 



Guinea-pigs, respectively killed by intraperitoneal injection of the 

 vibrio of cholera and of typhoid bacillus, were each nailed up in 

 a wooden box, and the boxes were buried in powdered sand. After 

 28 days the peritoneal material gave a negative result on culture, 

 no cholera vibrio occurring in one case, no typhoid bacillus in the 



1 Memorandum on the Sanitary Requirements of Cemeteries. Pp.8. Fol. 

 London, 1893. 



