REPORT OF COMMITTEE ON BACTERIOLOGICAL TECHNIC 139 



microscopic method. The dilution method (whereby a medium 

 is inoculated with progressively decreasing quantities of the 

 material under investigation until a dilution is reached too great 

 to contain any bacteria) is cumbersome and is not applicable 

 to many types of bacterial flora. The plate method and the 

 microscopic method, each with various modifications, are in 

 common use and can be appUed to a great variety of bacterial 

 habitats. Each method has its advantages and each its dis- 

 advantages; but by using both methods and properly comparing 

 the results, it is possible to obtain very good information as to 

 the actual number of bacteria in the material under investigation. 

 An admirable investigation of this sort, of the methods of count- 

 ing bacteria in milk, has recently been made by Breed and Stock- 

 ing (1920). 



Although milk has been investigated in this way more than 

 any other material, there are other natural habitats of bacteria 

 where it may be fully as important to know the best methods 

 of determining the actual numbers of organisms present as well 

 as to have official methods for routine use. There are, for 

 example: water, soil, sewage, vaccines, and various foodstuffs, 

 such as cheese, ketchup, butter, ice-cream, hamburg steak, 

 dried egg powder, and so forth. The field is too broad to cover 

 at once; but by attacking one problem at a time and by the 

 eventual estabfishment of various sub-committees, it is hoped 

 to round up the matter in time. 



Shortly after the appointment of the committee, the problem 

 of microorganisms in ketchup was referred to it. In this case the 

 work is practically limited to the microscopic method, as the 

 processing of the material kills the greater part of the organisms 

 originally present. Counting is difficult, and yet results are 

 important because they have already been used in the control 

 of this food industry. It was pointed out to the committee 

 that the industry would be glad to finance an investigation, but 

 wanted it entirely free from their influence. (The name of the 

 person or firm offering the money is not known to us.) The 

 matter was turned over to the New York Agricultural Experiment 

 Station, and it was found that they would gladly furnish the 



