48 BACTERIOLOGICAL METHODS 



mold contamination from the number of microscopic fields of the 

 compound microscope which show the presence of hyphal clusters, 

 is far from satisfactory. It indicates the amount of contamination 

 in a general way only. More reliable and more accurate estimates 

 could be obtained through the use of a counting apparatus in which 

 the number of hyphal clusters could be ascertained in definite 

 quantities of the material under examination. The hemacy- 

 tometer already mentioned does not serve the purpose because of 

 the smallness of the counting areas. The special counter described 

 in Fig. 5 would serve the purpose very well. It is furthermore 

 necessary to reduce the material to a uniform and standard fineness 

 by rubbing it through a sieve. A very small standard mesh sieve 

 would answer the purpose. Take i gram of the thoroughly mixed 

 material and by means of a small spatula rub all of it through the 

 sieve and make the estimations from the pulp which has been 

 passed through the meshes of the sieve. 



Precautions.- — The following are some of the factors which 

 necessitate caution in making counts of microbes, yeast cells, 

 spores and mold fragments. 



a. Badly decomposed factory pulp which compels prolonged 

 heating in order to render it suitable for canning, often presents 

 such a granular appearance as to make accurate counting of the 

 microbes rather difficult. In such materials many of the more 

 or less disintegrated pulp cells are filled with bacteria and these 

 cannot be included in the count. Commonly in such substances 

 many of the mold fragments are also very much disintegrated 

 through decomposition changes, probably initiated by enzymes 

 formed by the bacteria and other organisms. 



b. While it is quite easy to distinguish between living yeast 

 cells, dead yeast cells and spores, it is not thought advisable to 

 attempt such differentiation in routine laboratory practice, ex- 

 cepting in cases where identification is simple and where there is 

 very little room for doubt. One of the first important problems 

 for the food and drugs bacteriologist to solve is the identification 



