ii4 SCIENCE PROGRESS. 



action which enables the pest-bacilli to be recognised with 

 certainty. 



Infection by the bacillus in the majority of cases is at 

 the surface of the body, minute wounds and abrasions of 

 the skin affording a means of entrance. More rarely the 

 mucous membranes of the intestine are primarily affected, 

 and though Wilm believes the majority of cases in Hong 

 Kong were infected in this way, the reports of the various 

 commissions in Bombay state that this, though it may occur 

 is rarely seen. Experimentally animals may be infected at 

 the intestinal or respiratory surfaces and pest-bacilli are 

 frequently found in sputa and always in the excreta. Lesions 

 in the mouth or tonsils are also sites where the bacilli may 

 obtain an entrance into the body, but apparently these never 

 primarily infect by the mucous membrane of the stomach 

 (24). The cells lining the alimentary canal undoubtedly 

 oppose the entrance of bacteria. Most careful observa- 

 tions recently made by Neisser(26) show that chyle and 

 blood are absolutely free from germs even after the liberal 

 ingestion of pathogenic bacteria. The mesenteric glands 

 remain normal, and it is only when the mucous membrane is 

 diseased that bacteria can leave the cavity of the intestine, 

 and even then these are not absorbed, but grow through the 

 wall of the bowel in a manner comparable to the growth 

 which is known to take place through the substance of a filter. 

 Wilm and Abel have both examined the behaviour of 

 pest-bacilli in water, since it is conceivable that this may be 

 a vehicle for transmission of the specific germs. The 

 former observer found bacilli lived for twenty days in 

 distilled water, in spring water sixteen, and in sea water 

 six days, 200 c.c. of water being mixed with .5 c.c. of an 

 agar culture. Abel's researches also show that the specific 

 microbes of plague can live for weeks in water, so that by 

 washing in this there will be a possible risk of infection. 

 Gaffky and his colleagues however have shown that in 

 absolutely sterile water the bacilli live only three days and 

 in ordinary tap-water for one day, so that plague cannot be 

 considered to be a water-borne disease. 



The part played by insects in the spread of plague has 



