438 CONTAMINATION AND DETERIORATION OF FOOD 



ing of these foods, the microbiology of staleness and spoilage, and constructive meth- 

 ods for control. 



In our problem of maintaining fitness and soundness of such food we must take 

 note, then, of the initial load carried by the surface, the presence of commensal species 

 within the tissues, and the invading microbes incident to methods of preparation. 

 Soundness and safety call for control based upon intelligent appreciation of all these 

 factors and of the relative values of environmental factors such as cold, heat, evapora- 

 tion, or pickling upon these organisms. 



FRESH SOUND FOOD 



Our knowledge of the bacteriology of fresh sound food is largely empirical. It is 

 the common belief of the race that foodstuffs produced under the usual conditions, 

 gathered or harvested and found to be sound, i.e., to conform to those ideals of ap- 

 pearance, texture, odor, and flavor established as normal by experience, are fit for 

 food. We are just beginning to appreciate the number and variety of bacteria carried 

 upon the surfaces of these foods; these ordinarily prove harmless when the foods are 

 eaten fresh or submitted to methods of preparation dictated by race experience. Even 

 among these foods, we are beginning to find individual substances which occasionally 

 at least carry infections whose source was hitherto unsuspected. Thus our knowledge 

 of the microbic "load" initially present upon fresh food which shows no physical 

 marks of deterioration is actually inadequate for protection. Although race experi- 

 ence has established fairly safe systems of collecting, preparing, and consuming such 

 foods, there are inherent contaminations which are occasionally significant, beside the 

 grosser menace of contaminations due to congested populations — for example, the 

 sewage of great cities discharged into shellfish-producing waters, or the time, tem- 

 perature, and contact elements involved in long shipment lines followed by complex 

 systems of wholesale, jobbing, and retail distribution. 



CONTAMINATIONS OF HANDLING 



So long as the more perishable foodstuffs are largely consumed in the immediate 

 vicinity of production, the slogan of the home canners, "two hours from the garden 

 to the can," will carry the raw materials from the field to the table or to the status of 

 a preserved product practically unchanged. When commercial harvesting processes 

 are added and involve picking, packing in bulk, in baskets, hampers, crates, or bags, 

 transportation by truck or by rail, warehousing, jobbing, and finally the exposure in 

 the retail food stall, the initial bacterial content is supplemented greatly by the con- 

 tributions of numerous human agents, by the dust and filth of transportation, and 

 by contact with insects and vermin. From the point of view of safety, the bacterial 

 species added during such handling processes may often be far more important than 

 the initial load of micro-organisms. 



INCUBATION 



The factor of incubation is, as a rule, fully as significant as contamination. Few 

 natural food products (as distinct from manufactured products) in commercial con- 

 dition are entirely free from metabolic activities either in the form of en/ymic changes 



