GENERAL PRINCIPLES 179 



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 iu 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 those 

 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 Ballard. From the 

 careful study of a number of epidemics due to food poisoning, he . 

 was able, without the aid of modern bacteriology, to arrive at a 

 simple principle which must not be forgotten. Food poisoning is 

 due either to bacteria themselves or to their products, which are 

 contained iu 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 ingested 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 incuba- 

 tion period, the agents are probably bacteria. 



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

 isolated from poisoned foods some of the different species of bacteria 

 present.* It would appear that these are limited, as a rule, to two or 

 three kinds. As regards disease, the organisms of suppuration are 

 the most common. Liquefying or fermentative bacteria are fre- 

 quently present, the Proteus family being well represented. In 

 addition there are, according to circumstances, a number of common 

 saprophytes. Now, as we have pointed out, these organisms may 

 act injuriously by some kind of co-operation, or they may by them- 

 selves be harmless, and pathological conditions be due to the 

 occasional introduction of pathogenic species. 



The other fact requiring recognition from any one who proposes 

 to study the bacteriology of milk, or indeed of other foods, is, that a 

 not inconsiderable amount of the evil results of food poisoning 

 depends upon the tissues of the individual ingesting the food. 



* Report of Medical Officer to Local Oovernment Board, 1895-96, Appendix, 



