28 SCIENCE PROGRESS 



with the domestic sewage of great human communities. Even 

 if we had no direct evidence that they were capable of acting 

 as the carriers of such diseases, as enteric fever, which are spread 

 by water-borne infection, there would still be an d priori case 

 for this assumption. 



There is, of course, a strong body of evidence that establishes 

 the fact that all three species of shellfish do actually convey 

 enteric fever. Oysters, mussels, and cockles share with fruit, 

 milk, and vegetables the condition of being foods that are eaten 

 raw. The shellfish are, indeed, cooked to a certain extent, but 

 large quantities are eaten in this country just as they are taken 

 from the fishing grounds. Oysters are nearly always eaten in 

 the uncooked condition, yet the risk of the transmission of 

 epidemic disease attending the use, as human food, of this 

 mollusc is now relatively small, and this is because the higher 

 value of the oyster has led to much greater care in the selection 

 of storing places for the relaying of the shellfish before being 

 sent to the market. The cockle is rather less exposed to sewage 

 pollution than the mussel, but it has been shown that it can be 

 a cause of conve}^ance of enteric fever. Mussels are the most 

 abundant, by far, of the three species of molluscs and they are 

 the cheapest. Enormous quantities are (or used to be) sent 

 to the poorer quarters of the great towns, and there is now 

 little doubt that disease is to be traced to their consumption. 



Various ailments can so be traced. Mussel-poisoning — a 

 rather obscure affection, not well described — may result from 

 the consumption of healthy unpolluted mussels : it is due to 

 the presence of a toxin (mytilotoxin) which is apparently 

 normally present in the tissues of the animal, but which affects 

 only a small proportion of people displaying some kind of 

 idiosyncrasy. Gaertner-poisoning, also produced by eating 

 raw mussels, seems to be due to a bacterial infection ; it is 

 characterised by diarrhoea appearing very soon after con- 

 sumption of the shellfish. Finally there is enteric fever, which 

 appears after an incubation period of about a fortnight, but 

 which may be much less in the case of mussels acting as the 

 medium. Now the evidence of the conveyance of enteric by 

 shellfish taken altogether is fairly strong, but taken case by case 

 it does not seem to be easily established. Practically the only 

 evidence that a particular case of enteric fever is to be traced 

 to the consumption of shellfish is that the patient consumed 



