BACTERIA IN FOODS 1 79 



upon some important habits and effects of microbes. There 

 can be little doubt that food-bacteria afford an example. of 

 association and antagonism of organisms to which reference 

 has already been made. Any information that can be 

 gleaned to illumine these abstruse questions would be very 

 welcome at the present time. But there is a still further, 

 and possibly an equally important, point to bear in mind, 

 namely, the economic value of microbes in food. In a short 

 account like the present it will be impossible to enter into 

 hypotheses of pathology, but we shall at least be able to 

 consider some of these interesting experiments which have 

 been conducted in the sphere of beneficial bacteria. 



The injurious effects of organisms contained in foods has 

 been elucidated by the excellent work of the late Dr. Bal- 

 lard. From the careful study of a number of epidemics due 

 to food poisoning, this patient observer was able, without 

 the aid of modern bacteriology, to arrive at a simple prin- 

 ciple which must not be forgotten. Food poisoning is due 

 either to bacteria themselves or to their products, which are 

 contained in the substance of the food. In cases of the first 

 kind, bacteria gaining entrance to the human alimentary 

 canal, set up their specific changes and produce their toxins, 

 and by so doing in course of time bring about a diseased 

 condition, with its consequent symptoms. On the other 

 hand, if the products, sometimes called ptomaines, are in- 

 gested as such, the symptoms set up by their action in the 

 body tissues appear earlier. From these facts Dr. Ballard 

 deduced the simple principle that if there is no incubation 

 period or, at all events, a comparatively short space of time 

 between eating the poisoned food and the advent of disease, 

 the agents of the disease are products of bacteria. If, on the 

 other hand, there is an incubation period, the agents are 

 probably bacteria. 



It is necessary to mention two other facts. Dr. Cautley ' 



^ Report of Medical Officer to Local Government Board ^ 1895-1896, Appendix. 



