EXPERIMENT STATION BULLETINS. 403 



called the small irregular yeast. Besides this type, there was another more 

 distinct kind of yeast with perfectly round cells, all of which seemed to be- 

 long to the same species. 



The large, dull, convex yeasts were all rapid liquefiers, and the morphology 

 was very much the same in all cultures. The pink yeasts did not show re- 

 markable differences. They were always found in such small numbers 

 that we did not pay very much attention to them, since they were either 

 contaminations of the plates, or of the butter, and certainly had nothing to 

 do with the keeping quality of the butter. 



After we had grouped the yeasts as far as possible in the above-mentioned 

 types, there were more than forty cultures left ; these were transferred in 

 wort and some of them caused a fermentation of maltose, the rest were trans- 

 ferred onto wort gelatin, orcUnary gelatin, and finally on slant agar and 

 most of them could now be identified as small irregular yeasts^ Only a very 

 few were left as different from all previously described forms. 



The large, dull, convex yeast colonies on the original agar plates all belonged 

 to the same kind of yeast, but the round, smooth, glistening, and the small, 

 star-shaped colonies belong to three different groups, the small irregidar, the 

 -perfectly round, and the maltose fermenting yeasts. For this reason, the 

 counts of these types are certainly not exact, because in many cases two 

 cUfferent kinds are counted as only one species, e. g., Xa, XYla^, XXIIag, O3, 

 but since it was impossible to see any difference in the form of agar colonies 

 we must be satisfied ^ith these results of probability. 



All of our yeasts were non-spore-producers. They certainly do not be- 

 long to the genus Saccharomyces. We classify the yeasts as follows: 



White Yeasts. — Liquefying. 



Rapidly liquefying. 

 Slowly liquefying. 

 Pure white. 

 Cream white. 

 Non-liquefying. 



Small irregular. 

 Perfectly round. 

 Maltose fermenting. 

 Pink Yeasts. 



The rapidly liquefying yeast is a scum yeast with large cells. Usually 

 the larger ones are elliptic, 4 x 6/<, 5 x 6/i, sometimes to 6 x lOfi; the smaller 

 are round and 3 x 3/i to 4 x 4//. The agar streak culture is dull. After 

 3 weeks crystals appear in the nutrient agar and lactose agar. The agar 

 turns hght brown. The gelatin is rapidly liquefied. After one day the 

 liquefaction is usually saccate and later becomes stratiform. Milk is curded 

 after 2 or 3 days and rapidly digested at neutral reaction. On other liquid 

 media, as broth, wort and so on, a dry scum is formed, the liquid is turbid 

 and there is much sediment. There were, in all, 26 cultures of this kind 

 isolated. 



The white, slowly liquefying yeast resembles somewhat the rapidly liquefy- 

 ing kind. It is only found twice in two different tubs of butter sample 

 XVIII. The cells are almost rectangular and very large, 4 x 8-4 x 16/z, 

 a few smaller ones, 4 x 5 or 4 x 6/<, are elliptic; the cells are mostly granulated 

 and have no vacuoles. They begin to liquefy gelatin slowly after 2 days 

 of growth. The agar culture is not different from that of the rapidly liquefy- 

 ing yeast. Milk is curded and peptonized at neutral reaction. 



