FILTRATION OF CULTURES 73 



the incubator as quickly as possible, as cold has an injurious 

 effect on the organisms. If the inoculations have been made 

 at some distance from the laboratory, the plates should be 

 carried in an apparatus with a hot-water jacket — a bag con- 

 taining a hot-water bottle is often sufficient. 



The Bacteriological . Examination of Urine. — In such an 

 examination care must be taken to prevent the contamination 

 of the urine by extraneous organisms. In the male, specimens 

 withdrawn by a sterile catheter into a sterile vessel are pre- 

 ferable, but it is often sufficient to wash thoroughly the glans 

 penis and the meatus with . 1-1000 corrosive sublimate — the 

 lips of the meatus being everted for more thorough cleansing ; 

 the urine is then passed into a series of sterile flasks, the first 

 of which is rejected in case contamination has occurred. In 

 the female, after similar precautions as regards external 

 cleansing, the catheter must be used. The latter must be 

 boiled for half an hour, and anointed with olive oil sterilised 

 by half an hour's exposure in a plugged flask to a temperature 

 of 102° C. Here, again, it is well to reject the urine first 

 passed. It is often advisable to allow the urine to stand in a 

 cool place for some hours, to then withdraw the lower portion 

 with a sterile pipette, to centrifugalise this, and to use the 

 urine in the lower parts of the centrifuge tubes for microscopic 

 examination or for culture. 



Filtration of Cultures. — For many purposes it is necessary 

 to filter all the organisms from fluids in which they may have 

 been growing.. This is done especially in obtaining the soluble 

 toxic products of bacteria. The only filter capable of keeping 

 back such minute bodies as bacteria is that consisting of a tube 

 of unglazed earthenware as introduced by Chamberland. The 

 efficiency of such a filter depends on the fineness of the grain 

 of the clay from which it is made ; the finest is the Kitasato 

 filter and the Chamberland "B" pattern; the next finest is 

 the Chamberland " F " pattern, which is quite good enough for 

 ordinary work. The Doulton porcelain filter is also very suitable 

 and efficient. There are several types of filters, differing slightly 

 in detail, all possessing the common principle. Sometimes the 

 fluid is forced through the porcelain' tube. In one form, used for 

 obtaining sterile water, the filter consists practically of an ordinary 

 tap screwed into the top of a porcelain tube. Through the latter 

 the fluid is forced, and passes into a chamber formed by a metal 

 cylinder which surrounds the porcelain tube. The fluid escapes 

 by an aperture at the bottom. Such a filter is very suitable 

 for domestic use, or for use in surgical operating-theatres. As 



