208 AIDS TO BACTERIOLOGY 



at exceptional tides, and sometimes even with ordinary 

 tides, are covered at high- water. These animals (and not 

 least among them the geese) deposit on the marsh-lands 

 a very large amount of excrement, which is washed off 

 the marsh-lands at high-water. Cockles and mussels 

 especially abound in the vicinity of these grazing grounds, 

 which are often intersected by creeks. The sand in these 

 creeks will often be found quite black under the surface, 

 and even the shells of the cockles quite discoloured, and 

 yet there may be no sewer outfall within several miles.' 



Letts attributed the excess of Ulva latissima in Belfast 

 Lough as being due to its sewage-polluted waters. Nash, 

 however, demonstrated that Ulva latissima may be found 

 in creeks or on shores adjacent to extensive tracts of low- 

 lying marsh-lands which are used for grazing purposes, 

 but yet miles from any large sewer outfall. He therefore 

 concluded its presence on mussels to be no indication of 

 a polluted source. 



The Bacteiiology of Meat. 



In addition to examination for trichina, vermes, etc. 

 meat may have to be examined for tuberculosis and other 

 animal diseases which are dealt with under their re- 

 spective monographs, or for organisms causing food 

 poisoning (see B. enteritidis, p. 93, B. botulinus, p. 83, 

 B. paratyphosus ft, p. 95, and B. suipestifer, p. 96). A 

 filterable virus, a variant of B. coli,B. proteus, and JStaphy- 

 lococcus pyogenes aureus, have also been described as organ- 

 isms producing food poisoning. The isolation of proteus 

 from suspected material, even if it gives a positive agglu- 

 tination, requires cautious consideration before it is 

 connected with the disease, as McWeeney has shown that 

 it tends to undergo auto-agglutination. 



Varieties of Phycomyces, Penicillium, Mucor, Verti- 

 cillium, and Oospora, are the principal moulds that are 

 found on refrigerated meat. ' Red spot ' is due to 

 B. prodigiosus, and Cladosporium herbarum, causing ' black 

 spot/ is frequent. Klein investigated some brown spots 

 on frozen meat, and found a variety of yeast. Experi- 

 ments with animals showed that the yeast was not harm- 

 ful. Black spots are sometimes present in Argentine 

 beef on the lower or thin parts of fascia, in the fatty 

 portion of the thick parts, and in the fat belonging to 



