1 6 STORRS AGRICULTURAL EXPERIMENT STATION. 



If these facts are true it follows that the study of the develop- 

 ment of the species of bacteria in milk is a matter likely to be 

 of great importance in giving data for determining the whole- 

 someness of milk, and any facts which can be given bearing 

 upon this general subject will be contributions toward the solu- 

 tion of problems connected with the use of milk. 



The reason that such studies have not been hitherto carried 

 out is doubtless chiefly the difficulty of the study. To make 

 a quantitative test of bacteria in milk is very eas}^ but to 

 determine what species are present is much more difficult and 

 requires a long stud}^ of each individual sample; and to deter- 

 mine the percentage of each species present in the whole sample 

 of milk has been hitherto practically an impossibility. The 

 only method that can be used is that of making ordinary bac- 

 teriological plates and then carefully counting colonies on the 

 plates. It is well known to all bacteriologists that, whereas it 

 is possible by study of such plates to differentiate certain species 

 of bacteria from each other, a complete differentiation is quite 

 impossible. Many species of bacteria produce colonies upon 

 gelatin plates which are so closely alike that they cannot be 

 distinguished, and thus it is quite impossible to determine what 

 proportion of all bacteria present may belong to one species and 

 what proportion to another. The difficulties of such a line of 

 study have been so great that it has never been followed be- 

 yond the differentiation of a few simple characteristic types. 

 De Freudenreich, Russell and Winzirl, and Harrison, have 

 studied the proportion of lactic bacteria in cheese, and Jensen* 

 has in a similar wa}' made estimations of the number of a few 

 species of organisms present in butter. But beyond some slight 

 differentiation of a few characteristic forms, no work of this 

 kind has hitherto been attempted. 



In the laboratory at Wesleyan University there has been 

 developed during the last three or four years a method of 

 studying milk bacteria which enables us to make a moderately 

 satisfactory differentiation of species from each other. This 

 method, which was devised several 3'ears ago, has been in 

 constant use in our work, and the more it has been used the 

 more we have been convinced that it enables us to separate 

 species from each other in a manner superior to that in which 



*Centbl. f. IJact. u. Par. II., VIII., 1902, p. 11. 



